Animal Biology And Ecology

Marius ILIE,

Narcisa MEDERLE, Ion OPRESCU, Sorin MORARIU

Animal biology and ecology

Textbook of practical work for students of Veterinary Medicine

Discover the roles every organism has a role to play in its ecosystem and the structures and behaviors that allow it to survive

General notions – terminology

Ecology of parasites is a branch of general ecology studying parasite-host relationship, the influence of environmental factors on them, general and/or specific parasitic pollution limiting measures and ecosystem remediation.

Parasitism is a non-mutual relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host.

The parasitism phenomenon has been observed since ancient times and has been defined by many scientists. The host is source of food, biotope and protection for the parasite, therefore the relationship is benefical for him.The effect is detrimental or even lethal for the host instead.

Traditionally parasite referred to organisms with lifestages that needed more than one host (e.g. Taenia solium). These are now called macroparasites (typically protozoa and helminths). Parasitism is a relationship between two species of plants or animals in which one benefits at the expense of the other, sometimes without killing it.

Parasitism is differentiated from parasitoidism, a relationship in which the host is always killed by the parasite. Parasitoidism occurs in some ants, wasps, bees, flies, a few butterflies and moths. The female lays her eggs in or on the host, upon which the larvae feed on hatching.

Parasites may be characterized as ectoparasites—including ticks, fleas, leeches, and lice—which live on the body surface of the host and do not themselves commonly cause disease in the host; or endoparasites, which may be either intercellular (inhabiting spaces in the host’s body) or intracellular (inhabiting cells in the host’s body). Intracellular parasites—such as bacteria or viruses—often rely on a third organism, known as the carrier, or vector, to transmit them to the host.

Parasitic ecology presents interrelations with several disciplines close to its profile.

Ecoparazitological studies aim the understanding of pathogenic mechanisms, of environment survival ways of the parasitic elements and of the ecological interventions efficiency.

Parasites may have a single host, two hosts, three hosts or, more rarely, four hosts.

The developing process of the parasites that includes egg-adult stages is called life cycle.

A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction.

Asexual reproduction (fig. 1.1) is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only; it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. The offspring will be exact genetic copies of the parent.

Fig. 1.1. Asexual reproduction

Common forms of asexual reproduction include:

Budding

In this form of asexual reproduction, an offspring grows out of the body of the parent.

Hydras exhibit this type of reproduction.

Gemmules (Internal Buds)

In this form of asexual reproduction, a parent releases a specialized mass of cells that can develop into offspring.

Sponges exhibit this type of reproduction.

Fragmentation

In this type of reproduction, the body of the parent breaks into distinct pieces, each of which can produce an offspring.

Planarians exhibit this type of reproduction.

Regeneration

In regeneration, if a piece of a parent is detached, it can grow and develop into a completely new individual.

Echinoderms exhibit this type of reproduction.

Parthenogenesis

This type of reproduction involves the development of an egg that has not been fertilizedinto an individual.

Animals like most kinds of wasps, bees, and ants that have no sex chromosomes reproduce by this process. Some reptiles and fish are also capable of reproducing in this manner.

Sexual reproduction is a process that creates a new organism by combining the genetic material of two organisms; it occurs both in eukaryotes and in prokaryotes. In sexual reproduction, two individuals produce offspring that have genetic characteristics from both parents. Sexual reproduction (fig. 1.2) introduces new gene combinations in a population.

Fig. 1.2. Human embryogenesis

In a life cycle there are several types of hosts:

definitive (D.H.) – the body that carry the parasitic imaginal stage or sexual phase of protozoan

intermediate (I.H.) – the body that carry the parasitic preimaginal stages or asexual stage of the parasites

paratenic (P.H.) – bodies randomly involved in the development of a parasite and who ensure their survival and accumulation

vector (V.H.) – bodies that ensure survival and transport of parasites for appreciable distances.

Depending on the number of hosts, biological cycle may be:

Monoxenous – parasite needs a single host

Heteroxenous:

Dixenous (monoheteroxenous) – two hosts: GD + GI

Trixenous (diheteroxen) – three hosts: GD + 2G.I.

Tetraxenous (triheteroxenous) – four hosts: GD + 3G.I.

Autoheteroxenous – all forms of evolution are in the same host.

Hosts can be:

permissive

susceptible

resistent

paratenic

Depending on the time spent on the host, parasites can be:

permanent parasites

intermittent parasites

temporary parasites

Depending on the number of host species, parasites can be classified in:

holoxenic parasites (homoxenus, oioxenous)

stenoxenous parasites

oligoxenous parasites

eurixeneous parasites (ubiquist)

Host contamination can be done by different ways:

digestive

milk

transcutaneous

transplacental

Parasitism occurs very frequently in the animal world and this is why it is difficult to make a classification.

However terms of obligativity, stages and periods of time, parasitism can be:

obligatory,

non-obligatory.

Obligatory parasitism is when the parasitary life is an obligatory condition for at least one of the evolutive stages of a parasite. The host is a necessity for the parasite to exist or in its absence the life cycle is endangered.

According to the length of time, parasitism can be:

temporary,

stationary.

Temporary parasitism is typical to the parasites poorly adapted to parasitary life which tend to rely on the host only for food. This aspect is found in hematophagous arthropods (ticks, culicidae, simulidae, tabanidae) which can attack numerous species of animals and the man.

The stationary parasitism is an association where the host species is a food source and habitat for parasites for a short term.

This kind of parasitism could be:

periodically stationary,

permanently.

The periodic parasitism can be of larvae and imaginal type. The larvar type is when only the larvae have adapted to the parasity life while adults live free in specific biotopes.

►The larvar parasitism is found in some nematodes and insects whose larvae infest the fishes, birds and mammals. The insects Hypoderma bovis and Oestrus ovis infest in the larvar stage the subcutaneous conjunctive tissue from the dorsolumbar region of the taurine as well as the nasal cavities and the sinuses of the sheep. Adults live free, of short span of time, during summer until reproduction is completed.

►The imaginal parasitism is found when the adults adapted to the parasity life and the preimaginal forms live free in different ecosystem. Within the periodic parasitism other evolutive modes can be found, too, characterized by an alteration of parasite with free generations. For instance, in the trematode Fasciola hepatica there are two parasitary stages which alternate with two free stages.

The survival and development of some evolutive forms in the environment is an essential condition in the evolution of the parasites adapted to the temporary and periodic parasitism.

The permanent parasitism is a model of interspecific association where the parasite species adapted exclusively to the parasite life, the host organism being a habitat. The transfer of information, energy and substance from the environment to the parasite is done by interposition of the host. All of the forms or stages of parasite evolving take place only in the host organism.

In some cases, the evolutive forms develop in a single host (Trichinela spiralis – adults live in intestine and the larvae in the striated muscles in the same host).

In other cases, the complete evolution of the life cycle is achieved by the obligatory change of two hosts (babesia, to develop, needs the presence of vertebrates but also of ixodidea artropodes).

The obligatory parasitism also includes hyperparasitism by which a parasite becomes the host of another parasite. For the host, parasite cohabitation can become harmful or even deadly. This thing could be taken advantage of by post control in agriculture or getting rid of parasites in man and animals, that is why it is called biological control (fighting).

Hyperparasitism is also found in protozoa and insects. Thus, Histomonas meleagridis lives inside and in the eggs of the nematode Heterakis gallinae which infects the digestive tube (cecum) of the gallinaceums together with H. meleagridis.

Another example of hyperparasitism is in Dipylidium caninum, an intestinal cestode in carnivore, its larvar stage developing inside the fleas Ctenocephalides canis and Pulex iritans.

The non – obligatory parasitism is an incidental form by which some organisms living free in the environment can adapt to the parasite life.

This process is favored:

by the genetic and ecologic flexibility of a specie,

by the easy way of getting inside an organism of other species.

The capacity of adaptation of the non – obligatory parasites allows them to use energonutritive and information resources of the host and therefore survive.

This kind of parasitism is found in dipteral (muscidae) which can lay eggs or larvae on the body or natural cavities of animals, helping the development of the larvae in parasite conditions.

The creation of numerous breeds of sheep whit high zooproductive index (big production of fine wool and meat) paved the way for secondary morphophysiological characteristics (abundant sebaceous secretion, smooth skin and easily injured) which are an attractive factor for the muscidae of Lucilla, Calliphora and Phormya genii. These muscidae prefer the cutaneous biotopes of sheep where they lay eggs which leads to the enzootic evolution of cutaneous blow fly strike.

Schwerdtfeger model of tuning numbers in population with abiotic factors, density independent

Population – group of individuals of the same species living in the same territories and can reproduce among themselves.

Population demographic variables:

1. Number (population abundance): total number of individuals entering a population at a time, per unit area:

actual number

absolute number

2. Density: number of individuals or population biomass per unit surface or volume:

gross density (dB) – the ratio between the number of individuals (N) and area occupied by that population (S): dB=N/S

ecological density (ED) – the ratio between the number of individuals (N) and the usable area of an ecosystem (Su): dE=N/Su

3. Birth rate (Rλ) – birth ratio (λ) and the total number of individuals (N): Rλ=λ/N

4. Mortality rate (Rμ) – the ratio between the number of individuals killed in a time (μ) and the total number of ndividuals (N) Rμ=μ/N

5. Numerical growth rate (Rq) – the difference between births and deaths: Rq = Rλ-Rμ.

Each population is subjected to small amplitude oscillations, under the influence of biotic and abiotic factors.

Schwerdtfeger imagined a numerical adjustment of a population by density independent abiotic factors.

This model demonstrates that the number of individuals in a population is maintained in optimal limits by action of adverse climatic factors. Other factors (e.g. food) can not effectively regulate the population density.

Wisarcot modeling of mutual adjustment of primary and secondary consumers level in a biocenosis

Biocenosis – a group of living beings which corresponds to the composition, number of species and individuals to certain environmental conditions, this group is linked by mutual dependent reproduction in a secure place and in a permanent way. Biocenotic components occupy a space – biotope.

Relationships established between biocenotic components are direct or indirect, trophic or defense dependence.

Wisarcot imagined the way of mutual adjustment of the primary consumers (C1) and secondary consumers (C2) level, simplifying biocenosis in two structural components.

Maintaining of dynamic equilibrium state is achieved respecting a few rules:

Minimum rule

Maximum rule

Specific start rule

Accidental couples rule

Specific descent rule

Information translation rule.

Based on numbers evolution analysis of prey-predator populations were stated three laws of deterministic nature:

1. Number of predator and prey individuals remains constant, despite fluctuations continue.

2. Prey and predator individual fluctuations are periodic.

3. If prey-predator system is disrupted by the action of an environmental factor that reduces the number of both elements, a period of recovery in the number of individuals is following. After termination of the disturbing factor, the prey population recovers much faster than the predator population.

Ecobiology of protozoa

Protozoa are a diverse group of unicellular eukaryotic organisms, many of which are motile. Originally, protozoa had been defined as unicellular protists with animal-like behavior, e.g., movement.

Protozoan, organism, usually single-celled and heterotrophic (using organic carbon as a source of energy), belonging to any of the major lineages of protists and, like most protists, typically microscopic.

All protozoans are eukaryotes and therefore possess a “true,” or membrane-bound, nucleus. They also are nonfilamentous (in contrast to organisms such as molds, a group of fungi, which have filaments called hyphae) and are confined to moist or aquatic habitats, being ubiquitous in such environments worldwide, from the South Pole to the North Pole. Many are symbionts of other organisms, and some species are parasites.

The Protozoa are considered to be a subkingdom of the kingdom Protista, although in the classical system they were placed in the kingdom Animalia. More than 50,000 species have been described, most of which are free-living organisms; protozoa are found in almost every possible habitat.

Anton van Leeuwenhoek was the first person to see protozoa, using microscopes he constructed with simple lenses.

Some species are considered commensals, i.e., normally not harmful, whereas others are pathogens and usually produce disease. Many protozoan infections that are inapparent or mild in normal individuals can be life-threatening in immunosuppressed patients, particularly patients with acquired immune deficiency syndrome (AIDS).

Examples of pathogenic protozoa: Toxoplasma gondii, a very common protozoan parasite, usually causes a rather mild initial illness followed by a long-lasting latent infection. AIDS patients, however, can develop fatal toxoplasmic encephalitis. Cryptosporidium was described in the 19th century, but widespread human infection has only recently been recognized. Cryptosporidium is another protozoan that can produce serious complications in patients with AIDS.

Terminology

Following the Greek root of the name cillia, the singular form is protozoon /proʊtəˈzoʊ.ɒn/. Its use has, however, partially been replaced by the word protozoan, which was originally only used as an adjective. In the same manner the plural form protozoans is sometimes being used instead of protozoa.

Protozoa is sometimes considered a subkingdom. It was traditionally considered a phylum under Animalia referring to unicellular animals, with Metazoa referring to multicellular animals.

Morphological characteristics

Protozoa commonly range from 10 to 52 micrometers, but can grow as large as 1 mm, and are seen easily by microscope. The largest protozoa known are the deep-sea dwelling xenophyophores, which can grow up to 20 cm in diameter. The smallest (mainly intracellular forms) are 1 to 10 μm long, but Balantidium coli may measure 150 μm.

Protozoa are unicellular eukaryotes. As in all eukaryotes, the nucleus is enclosed in a membrane. In protozoa other than ciliates, the nucleus is vesicular, with scattered chromatin giving a diffuse appearance to the nucleus, all nuclei in the individual organism appear alike. The ciliates have both a micronucleus and macronucleus, which appear quite homogeneous in composition.

The organelles of protozoa have functions similar to the organs of higher animals. The plasma membrane enclosing the cytoplasm also covers the projecting locomotory structures such as pseudopodia, cilia, and flagella. The outer surface layer of some protozoa, termed a pellicle, is sufficiently rigid to maintain a distinctive shape, as in the trypanosomes and Giardia. However, these organisms can readily twist and bend when moving through their environment.

In most protozoa the cytoplasm is differentiated into ectoplasm (the outer, transparent layer) and endoplasm (the inner layer containing organelles); the structure of the cytoplasm is most easily seen in species with projecting pseudopodia, such as the amebas.

Some protozoa have a cytosome or cell “mouth” for ingesting fluids or solid particles. Contractile vacuoles for osmoregulation occur in some, such as Naegleria and Balantidium.

Many protozoa have subpellicular microtubules; in the Apicomplexa, which have no external organelles for locomotion, these provide a means for slow movement. The trichomonads and trypanosomes have a distinctive undulating membrane between the body wall and a flagellum. Many other structures occur in parasitic protozoa, including the Golgi apparatus, mitochondria, lysosomes, food vacuoles, conoids in the Apicomplexa, and other specialized structures. From the point of view of functional and physiologic complexity, a protozoan is more like an animal than like a single cell. Figure 4.1. shows the structure of the bloodstream form of a trypanosome, as determined by electron microscopy.

Pellicle

The pellicle is a thin layer supporting the cell membrane in various protozoa, protecting them and allowing them to retain their shape, especially during locomotion, allowing the organism to be more hydrodynamic. They vary from flexible and elastic to rigid. Although somewhat stiff, the pellicle is also flexible and allows the protist to fit into tighter spaces. In ciliates and Apicomplexa, it is formed from closely packed vesicles called alveoli. In euglenids, it is formed from protein strips arranged spirally along the length of the body. Examples of protists with a pellicle are the euglenoids and the paramecium, a ciliate.

The pellicle consists of many bacteria that adhere to the surface by their attachment pili. Thus, attachment pili allow the organisms to remain in the broth, from which they take nutrients, while they congregate near air, where the oxygen concentration is greatest.

Fig. 4.1. Fine structure of a protozoan parasite, Typanosoma evansi, as revealed by transmission electron microcopy of thin sections

Motility and digestion

Protozoans are motile; nearly all possess flagella, cilia, or pseudopodia that allow them to navigate their aqueous habitats. However, this commonality does not represent a unique trait among protozoans; for example, organisms that are clearly not protozoans also produce flagella at various stages in their life cycles (e.g., most brown algae). Others do not move at all.

Protozoans are also strictly non-multicellular and exist as either solitary cells or cell colonies.

Protozoa may absorb food via their cell membranes, some, e.g., amoebas, surround food and engulf it, and yet others have openings or "mouth pores" into which they sweep food, and that engulfing of food is said to be phygocytosis. All protozoa digest their food in stomach-like compartments called vacuoles.

Nutrition

The protozoans are unified by their heterotrophic mode of nutrition, meaning that these organisms acquire carbon in reduced form from their surrounding environment.

The nutrition of all protozoa is holozoic; that is, they require organic materials, which may be particulate or in solution. Amebas engulf particulate food or droplets through a sort of temporary mouth, perform digestion and absorption in a food vacuole, and eject the waste substances.

Many protozoa have a permanent mouth, the cytosome or micropore, through which ingested food passes to become enclosed in food vacuoles.

Pinocytosis is a method of ingesting nutrient materials whereby fluid is drawn through small, temporary openings in the body wall. The ingested material becomes enclosed within a membrane to form a food vacuole.

Protozoa have metabolic pathways similar to those of higher animals and require the same types of organic and inorganic compounds.

Many protists are mixotrophs, capable of both heterotrophy (secondary energy derivation through the consumption of other organisms) and autotrophy (primary energy derivation, such as through the capture of sunlight or metabolism of chemicals in the environment).

Some protozoans, such as Paramecium bursaria, have developed symbiotic relationships with eukaryotic algae, while the amoeba Paulinella chromatophora remarkably appears to have acquired autotrophy via relatively recent endosymbiosis of a cyanobacterium (a blue-green alga).

Many protozoans either perform photosynthesis themselves or benefit from the photosynthetic capabilities of other organisms. Some algal species of protozoans, however, have lost the ability to photosynthesize (e.g., Polytomella species and many dinoflagellates), further complicating the concept of protozoan.

Ecological role

As components of the micro- and meiofauna, protozoa are an important food source for microinvertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and algal production to successive trophic levels is important. As predators, they prey upon unicellular or filamentous algae, bacteria, and microfungi. Protozoa are both herbivores and consumers in the decomposer link of the food chain. They also control bacteria populations and biomass to some extent. Protozoa such as the malaria parasites (Plasmodium spp.), trypanosomes and leishmania, are also important as parasites and symbionts of multicellular animals.

Life cycle

During its life cycle, a protozoan generally passes through several stages that differ in structure and activity. Trophozoite (Greek for “animal that feeds”) is a general term for the active, feeding, multiplying stage of most protozoa.

Some protozoa have life stages alternating between proliferative stages (e.g., trophozoites) and dormant cysts. As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to survive outside of a host, and allows their transmission from one host to another. The conversion of a trophozoite to cyst form is known as encystation, while the process of transforming back into a trophozoite is known as excystation.

In parasitic species this is the stage usually associated with pathogenesis. In the hemoflagellates the terms amastigote, promastigote, epimastigote, and trypomastigote designate trophozoite stages that differ in the absence or presence of a flagellum and in the position of the kinetoplast associated with the flagellum.

A variety of terms are employed for stages in the Apicomplexa, such as tachyzoite and bradyzoite for Toxoplasma gondii. Other stages in the complex asexual and sexual life cycles seen in this phylum are the merozoite (the form resulting from fission of a multinucleate schizont) and sexual stages such as gametocytes and gametes.

Some protozoa form cysts that contain one or more infective forms. Multiplication occurs in the cysts of some species so that excystation releases more than one organism. For example, when the trophozoite of Entamoeba histolytica first forms a cyst, it has a single nucleus. As the cyst matures nuclear division produces four nuclei and during excystation four uninucleate metacystic amebas appear. Similarly, a freshly encysted Giardia lamblia has the same number of internal structures (organelles) as the trophozoite. However, as the cyst matures the organelles double and two trophozoites are formed. Cysts passed in stools have a protective wall, enabling the parasite to survive in the outside environment for a period ranging from days to a year, depending on the species and environmental conditions. Cysts formed in tissues do not usually have a heavy protective wall and rely upon carnivorism for transmission. Oocysts are stages resulting from sexual reproduction in the Apicomplexa. Some apicomplexan oocysts are passed in the feces of the host, but the oocysts of Plasmodium, the agent of malaria, develop in the body cavity of the mosquito vector.

Reproduction in the Protozoa may be asexual, as in the amebas and flagellates that infect humans, or both asexual and sexual, as in the Apicomplexa of medical importance (fig. 4.2, 4.3).

Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (e.g., Coccidia). An individual protozoan is hermaphroditic.

Fig. 4.2. Life cycle of protozoan flagellate

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages) . The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites) . In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites) . Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk . Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces . Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.

The most common type of asexual multiplication is binary fission, in which the organelles are duplicated and the protozoan then divides into two complete organisms.

Division is longitudinal in the flagellates and transverse in the ciliates; amebas have no apparent anterior-posterior axis.

Endodyogeny is a form of asexual division seen in Toxoplasma and some related organisms. Two daughter cells form within the parent cell, which then ruptures, releasing the smaller progeny which grow to full size before repeating the process.

In schizogony, a common form of asexual division in the Apicomplexa, the nucleus divides a number of times, and then the cytoplasm divides into smaller uninucleate merozoites. In Plasmodium, Toxoplasma, and other apicomplexans, the sexual cycle involves the production of gametes (gamogony), fertilization to form the zygote, encystation of the zygote to form an oocyst, and the formation of infective sporozoites (sporogony) within the oocyst.

Some protozoa have complex life cycles requiring two different host species; others require only a single host to complete the life cycle. A single infective protozoan entering a susceptible host has the potential to produce an immense population.

Fig. 4.3. Life cycle of coccidia

In 1985 the Society of Protozoologists published a taxonomic scheme that distributed the Protozoa into six phyla. They are Zoomastigophora, Rhizopoda, Apicomplexa, Ciliophora, Foraminifera, and Actinopoda.

Materials

Biological samples

Movies

Mode of work

Flotation method

Direct smear

Essentially the end of the paper outlined the general characteristics of Protozoa:

The members of the phylum Protozoa are acellular or noncellular or unicellular.

They are simplest and most primitive of all animals, with protoplasmic grade of organization.

Various parts of the protoplasm performing different function of the cell are called organelles.

These are minute microscopic organisms. They are either naked or covered by pellicle or shell.

The single cell of protozoans performs all function of life as in metazoans.

They are freeliving or parasitic or symbiotic or saprozoic or commensal organisms.

Free living Protozoa are mostly aquatic, inhabiting fresh and sea waters and damp places. Parasitic and commensal protozoans live over or inside the bodies of animals and plants. Sufficient environment is essential in their environment.

Certain protozoans are solitary while some exhibit colonial organization, but members of the colony never loose their individuality.

They do not show any of the types of body symmetry.

Locomotion is performed by organelles like pseudopodia, flagella or cilia.

The mode of nutrition is holozoic, holophytic, saprozoic, mixotrophic or parasitic.

Digestion occurs intracellularly inside the food vacuole

Respiration takes place by diffusion through body surface.

Excretion and osmoregulation are performed by contractile vacuoles and by body surface.

Responses to stimuli in these organisms give an indication of the beginning o\f the nervous system of higher animals.

Reproduction takes place by budding, binary fission, multiple fission (sporulation), syngamy, conjugation, endomyxis and autogamy.

Associated with the primitive organization these animals exhibit the power of regeneration.

Life history may be simple or complicated with alteration of asexual and sexual phases.

There is no natural death to these organisms since the parent is converted into two or more daughter individuals.

Encystment commonly occurs to help in dispersal as well as to resist unfavorable conditions of food temperature and moisture.

Ecobiology of trematodes (flukes)

Etymology

The Trematoda are a class of phylum Platyhelminthes (flatworms), which are commonly referred to as fluke. This term can be traced back to the Old English name for flounder, and refers to the flattened, rhomboidal shape of the worms.

The Platyhelminthes include various dorso-ventrally flattened animals that were consequently commonly described as flatworms which are typically bilaterally symmetrical.

The flukes can be classified into two groups, on the basis of the system which they infect in the vertebrate host (tissue flukes and blood flukes). They may also be classified according to the environment in which they are found. For instance, pond flukes infect fish in ponds.

Taxonomy and biodiversity

The trematodes or flukes comprises two subclasses, the Aspidogastrea and the Digenea, and are estimated to include 18,000 to 24,000 species. Nearly all trematodes are parasites of mollusks and vertebrates.

The monogeneans are typically (often economically important) ectoparasites of the skin and/or gills of fish, amphibians, reptiles, cetaceans or cephalopods; some species become endoparasitic by inhabiting the nose, the pharynx, cloaca, bladder etc. Formerly the Monogenea were included in Trematoda on the basis that these worms are also vermiform parasites, but modern phylogenetic studies have raised this group to the status of a sister class within the Platyhelminthes, along with the Cestoda.

The Aspidogastrea is a relatively small group, which is characterized by a very large hookless holdfast organ which, in adult worms, covers nearly the whole ventral side. The smaller Aspidogastrea, comprising about 100 species, are obligate parasites, typically endoparasites of many molluscs, elasmobranchs, teleosts, turtles, or decapod crustaceans and are not host specific. May also infect turtles and fish, including cartilaginous fish.

The Digenea, which constitute the majority of trematode diversity, are obligate parasites of both mollusks and vertebrates, but rarely occur in cartilaginous fish. The 6000 species of digenetic trematodes are very common and widespread parasites of all classes of vertebrates and may inhabit (as adult or juvenile worms) nearly every organ of their hosts. Externally they are characterized by a sucker around the mouth and an additional ventral sucker or acetabulum that is involved both in the attachment to host surfaces and in locomotion. The shape and location of these suckers is species-specific. Digenean development occurs in at least two different hosts and involves several generations.

Morphology

The structure of flukes is summarized in figures 5.1, and 5.2.

A dorsoventrally flattened body, bilateral symmetry, and a definite anterior end are features of platyhelminths in general and of trematodes specifically. Flukes are leaf-shaped, ranging in length from a few millimeters to 7 to 8 cm.

Fig. 5.1. Structure of flukes (A) Hermaphroditic fluke. (B) Bisexual fluke.

Their most distinctive external feature is the presence of two suckers, one oral sucker around the mouth and a ventral sucker or acetabulum that can be used to adhere to host tissues.

The body surface of trematodes comprises a tough syncitial tegument, which helps protect against digestive enzymes in those species that inhabit the gut of larger animals. The tegument is morphologically and physiologically complex. It is also the surface of gas exchange; there are no respiratory organs.

A body cavity is lacking. Organs are embedded in specialized connective tissue or parenchyma. Layers of somatic muscle permeate the parenchyma and attach to the tegument.

Flukes have a well-developed alimentary canal with a muscular pharynx and esophagus. The intestine is usually a branched tube (secondary and tertiary branches may be present) consisting of a single layer of epithelial cells. The main branches may end blindly or open into an excretory vesicle.

Although the excretion of nitrogenous waste occurs mostly through the tegument, trematodes do possess an excretory system, which is instead mainly concerned with osmoregulation. This consists of two or more protonephridia, with those on each side of the body opening into a collecting duct.

The excretory vesicle also accepts the two main lateral collecting ducts of the excretory system, which is of a protonephridial type with flame cells. A flame cell is a hollow, terminal excretory cell that contains a beating (flamelike) group of cilia. These cells, anchored in the parenchyma, direct tissue filtrate through canals into the two main collecting ducts.

Fig. 5.2. Some common adult liver flukes. EX, excretory bladder; GP, genital pore; GÖ, genital bulbus; HK, hooks, spines of tegument; IN, intestine; INC, intestine (cut off on drawing); LC,?Laurer's canal; OS, oral sucker; OV, ovary (?germarium); RS, receptaculum seminis; TE, testis; UT, uterus with eggs; VE, vas efferens of TE; VI, vitellary glands (vitellarium); VS, ventral sucker (acetabulum)

The two collecting ducts typically meet up at a single bladder, opening to the exterior through one or two pores near the posterior end of the animal.

The brain consists of a pair of ganglia in the head region, from which two or three pairs of nerve cords run down the length of the body. The nerve cords running along the ventral surface are always the largest, while the dorsal cords are present only in the Aspidogastrea. Trematodes generally lack any specialised sense organs, although some ectoparasitic species do possess one or two pairs of simple ocelli.

Reproductive system

Except for the blood flukes, trematodes are hermaphroditic, having both male and female reproductive organs in the same individual.

The male organ consists usually of two testes with accessory glands and ducts leading to a cirrus, or penis equivalent, that extends into the common genital atrium. Sperm ducts join together on the underside of the front half of the animal.This final part of the male system varies considerably in structure between species, but may include sperm storage sacs and accessory glands, in addition to the copulatory organ, which is either eversible, and termed a cirrus, or non-eversible, and termed a penis.

The female gonad consists of a single ovary, which is connected, via a pair of ducts to a number of vitelline glands on either side of the body, that produce yolk cells; with a seminal receptacle and vitellaria, that connect with the oviduct as it expands into an ootype. The tubular uterus extends from the ootype and opens into the genital atrium.

Both self- and cross-fertilization occur. The components of the egg are assembled in the ootype. Eggs pass through the uterus into the genital atrium and exit ventrally through the genital pore. This opens into an elongated uterus that opens to the exterior close to the male opening. The ovary is often also associated with a storage sac for sperm, and a copulatory duct termed Laurer's canal.

Fluke eggs, except for those of schistosomes, are operculated (have a lid).

Life Cycle

Except for some groups (e. g., the dioecious Schistosomatidae), flukes are hermaphroditic, utilizing sexual reproduction (with cross-insemination) in the final host (fig. 5.3).

These eggs leave the host in feces, urine, or sputum, and the zygote within the eggs develops (or has already developed by this stage) into a ciliated larva (miracidium).

In general this stage infects a gastropod mollusk or a lamellibranch (by penetration or via oral uptake) as first intermediate host, inside which a polyembryonic, mitotic reproduction occurs involving different developmental stages (sporocysts, rediae) and leading finally to the production of numerous motile and infective cercariae.

The latter leave the first intermediate host, often with a marked rhythm and, in some species, enter a second intermediate host or attach to the surface of plants, or in others directly penetrate the final host.

Inside the second intermediate host or on the surface of plants the cercariae encyst and develop into metacercariae; cyst walls are totally or partly produced by cystogenous glands in the cercarial apex.

The cercariae, which may possess a tail for swimming, develop further in one of three ways. They either penetrate the definitive host and transform directly into adults, or penetrate a second intermediate host and develop as encysted metacercariae, or they encyst on a substrate, such as vegetation, and develop there as metacercariae.

Fig. 5.3. Life cycles of the flukes Dicrocoelium dendriticum (A) and Paramphistomum cervi (B) in sheep and cattle.

Adult worms in the bile ducts (a) or rumen (B). 2 Eggs are excreted in feces fully embryonated (A) or not (B). 2.1 In P. cervi the finally formed miracidium hatches from the egg and enters a water snail, whereas in D. dendriticum land-living snails swallow the eggs containing the miracidium. 3±4 Intermediate hosts for P. cervi are water snails of the genera Bulinus, Planorbis, Stagnicola, and Anisus, whereas in D. dendriticum land snails of the genera Zebrina or Helicella are involved. Development in snails proceeds via two generations of sporocysts in D. dendriticum, whereas in P. cervi a sporocyst and two rediae occur. Finally, tailed cercariae are produced, which leave the snail (3) or are excreted by the snails within slime-balls (4.1), but remain immotile (4.2). 5±6 In D. dendriticum ants become second intermediate hosts when eating slime-balls. Most of the cercariae encyst in the hemocoel (6) as metacercariae and can then infect the final host. One or two cercariae enter the subesophageal ganglion, encyst there and cause an alteration of the ant's behavior. When the temperature drops in the evening hours, the infected ants climb to the tips of grass (and other plants) and grasp them firmly with their mandibles, while uninfected ants return to their nests. The infected ants remain attached until the next morning, when they warm up and resume normal behavior. These attached ants may be swallowed by plant-eating mammals. In P. cervi the free-swimming cercariae (with two eye spots) encyst on herbage and other objects (6), thus becoming metacercariae. Upon being swallowed along with forage, excystment of the metacercariae of both species occurs in the duodenum. From there they enter the bile duct (D. dendriticum) or return (via the intestinal wall) into the abomasum (P. cervi), and from there go to the rumen, where they attach among the villi. EY, eye spot; EX, excretory bladder; GB, germ balls; GP, genital pore; HD, head; IN, intestine; MC, metacercaria; MI, miracidium; OP, operculum; OS, oral sucker; OV, ovary; TA, tail; TE, testis; UT, uterus; VI, vitellarium; VS, ventral sucker

The metacercariae grow and become mature adults when orally ingested by the final host. When a metacercarial cyst is ingested, digestion of the cyst liberates an immature fluke that migrates to a specific organ site and develops into an adult worm. Inside the final host they feed on its fluids depending on their final habitat.

The blood flukes or schistosomes are the only bisexual flukes that infect humans. Although the sexes are separate, the general body structure is the same as that of hermaphroditic flukes. Within the definitive host, the male and female worms inhabit the lumen of blood vessels and are found in close physical association. The female lies within a tegumental fold, the gynecophoral canal, on the ventral surface of the male. The medically important flukes belong to the taxonomic category Digenea. This group of flukes has a developmental cycle requiring at least two hosts, one being a snail intermediate host. Depending on the species, other intermediate hosts may be involved to perpetuate the larval form that infects the definitive human host.

Ecobiology of tapeworms (cestodes)

In biology, tapeworms or cestodes comprise a class (Cestoda) of ribbon–like endoparasitic flatworms that live in the digestive tract of vertebrates as adults and often in the bodies of various animals (intermediate hosts) as juveniles (fig. 6.1, 6.2).

Fig. 6.1. Macroscopic aspect of tapeworm.

Fig. 6.2. Tapeworm parasites in small intestin

Tapeworm, also called cestode, any member of the invertebrate class Cestoda (phylum Platyhelminthes), a group of parasitic flatworms containing about 5,000 species.

Tapeworms are internal parasites, affecting certain invertebrates and the liver or digestive tracts of all types of vertebrates—including humans, domestic animals, and other food animals, such as fish.

Whereas flukes are flattened and generally leaf-shaped, adult tapeworms are flattened, elongated, and consist of segments called proglottids.

As flatworms the soft flatworm body is ribbon-shaped, flattened dorso-ventrally (from top to bottom), and bilaterally symmetric. They are acoelomates that are characterized by having three germ layers (ectoderm, mesoderm, and endoderm) and lacking respiratory and circulatory systems.

Cestodes are covered with a cuticle (tough but flexible, non-mineral covering), and lack a true circulatory or respiratory system; they do have a bilateral nervous system.

Tapeworms occur worldwide and range in size from about 1 mm (0.04 inch) to more than 15 m (50 feet). The largest tapeworms grow up to 60 feet and may have three to several thousand segments. However, the longest known tapeworm, Polygonoporus, which infects whales, can reach 40 m.

Anatomically, adult tapeworms typically are divided into a scolex, sometimes colloquially referred to as the "head,", which bears the organs of attachment, a neck that is the region of segment proliferation, and a chain of a few to large number of proglottids called the strobili (fig. 6.3).

These parasites are given the name "tapeworm," because their strobila look like a strip of tape.

The strobila elongates as new proglottids form in the neck region. The segments nearest the neck are immature (sex organs not fully developed) and those more posterior are mature. The terminal segments are gravid, with the egg-filled uterus as the most prominent feature.

As members of the platyhelminths, the cestodes, or tapeworms, possess many basic structural characteristics of flukes, but also show striking differences. Figure xxx shows the general features of the structure and development of tapeworms.

Scolex

The scolex or "head" is the anterior end of the worm and remains attached to the intestine of the definitive host. It is not bigger than the head of a pin, yet it works as the hold-fast of the parasite (fig. 6.4).

The scolex possesses a variety of adhesive structures including suckers and hooks which are used to adhere to the host.

Externally, the scolex is characterized by holdfast organs. Depending on the species, these organs consist of a rostellum, bothria, or acetabula.

Fig. 6.3. Structure of tapeworms.

A rostellum is a retractable, conelike structure that is located on the anterior end of the scolex, and in some species is armed with hooks.

In some groups, the scolex is dominated by bothria, which are sometimes called "sucking grooves," and function like suction cups. Bothria are long, narrow, weakly muscular grooves that are characteristic of the pseudophyllidean tapeworms.

Acetabula (suckers like those of digenetic trematodes) are characteristic of cyclophyllidean tapeworms.

Hooks and suckers to help in attachment. Cyclophyllid cestodes can be identified by the presence of four suckers on their scolex, though they may have rostellum and hooks.

Though the scolex is often the most distinctive part of an adult tapeworm, diagnosis is carried out by identifying eggs and gravid proglottids in feces, as the scolex remains hidden inside the patient.

Neck

The neck of a tapeworm is a well-defined, short, narrow, and unsegmented region behind the scolex. It is dorso-ventrally flattened and composed of a relatively undifferentiated mass of cells. It is the budding zone, growth zone, area of proliferation or area of segmentation, as it is here that new proglottids are formed.

Strobila

The proglottids are linearly arranged with identical internal structures – mostly reproductive. There is no gut and the nutrients are taken up by the epidermal cells.

The strobili forms the main bulk of the body and is composed of a linear series of segments or proglottids arranged in a chain-like fashion. However, they can be grouped into three different kinds, namely immature, mature, and gravid proglottids.

Immature proglottids are the anterior most ones just behind the neck. They are shorter and broader and are devoid of reproductive organs.

Mature proglottids occupy the middle part of the strobila and are squarish in outline. Tapeworms are hermaphrodite (male and female sex organs in the same individual) and protandrous (male maturing first), therefore, anterior mature proglottids consist of only male reproductive organs, while the posterior ones contain both male and female organs side by side. Thus a mature proglottid is a complete reproductive unit and produces eggs either by self-fertilization or cross-fertilization with other mature proglottids. It has been suggested by some early biologists that each should be considered a single organism, and that the tapeworm is actually a colony of proglottids.

Gravid proglottids occur in the posterior part of strobila and are longer than the width. These proglottids consist of no more reproductive organs than the highly branched uterus packed with fertilized eggs at different stages of development. The terminal gravid proglottids detach from rest of the body either singly or in small group by a process termed apolysis. This phenomenon serves to limit the length of the parasite and to transfer the developing embryo to exterior in feces of the host.

Fig. 6.4. The scolex (left) and a mature proglottid (right) of a typical cestode tapeworm (not to scale).

A characteristic feature of adult tapeworm is the absence of a digestive system, which is intriguing since all of these adult worms inhabit the small intestine. The lack of an alimentary tract means that substances enter the tapeworm across the tegument. This structure is well adapted for transport functions, since it is covered with numerous microvilli resembling those lining the lumen of the mammalian intestine. The pre-digested food in the host's small intestine is the chief source of nourishment for tapeworm. The general body surface of the parasite is greatly increased by the presence of microvilli. Therefore, the swift efficiency with which absorption takes place can be compared with the soaking action of blotting paper.

The excretory system is of the flame cell type. Their main excretory units are protonephric flame cells scattered all over the parenchyma of the body. The filtered excretory material is emptied into lateral longitudinal excretory canals extending the whole length of the body and thrown out through excretory pore at the end of the body.

The parasites lack respiratory organs as well, with respiration of the tapeworms being mainly anaerobic or anoxybiotic, with glycolysis being the chief respiratory pathway. When oxygen become available, the general body lining works as the respiratory surface.

The scolex contains the cephalic ganglion, or “brain,” of the tapeworm nervous system. All cestodes have nerve rings and lateral nerve cords passing through outthe length of the body.

Cestodes are hermaphroditic, each proglottid possessing male and female reproductive systems similar to those of digenetic flukes.

However, tapeworms differ from flukes in the mechanism of egg deposition. Eggs of pseudophyllidean tapeworms exit through a uterine pore in the center of the ventral surface rather than through a genital atrium, as in flukes.

In cyclophyllidean tapeworms, the female system includes a uterus without a uterine pore (fig. 6.4). Thus, the cyclophyllidean eggs are released only when the tapeworms shed gravid proglottids into the intestine. Some proglottids disintegrate, releasing eggs that are voided in the feces, whereas other proglottids are passed intact.

The eggs of pseudophyllidean tapeworms are operculated, but those of cyclophyllidean species are not. Eggs of all tapeworms, however, contain at some stage of development an embryo or oncosphere. The oncosphere of pseudophyllidean tapeworms is ciliated externally and is called a coracidium. The coracidium develops into a procercoid stage in its micro-crustacean first immediate host and then into a plerocercoid larva in its next intermediate host which is a vertebrate. The plerocercoid larva develops into an adult worm in the definitive (final) host. The oncosphere of cyclophyllidean tapeworms, depending on the species, develops into a cysticercus larva, cysticercoid larva, coenurus larva, or hydatid larva (cyst) in specific intermediate hosts. These larvae, in turn, become adults in the definitive host. Figure 6.5 illustrates these larval forms and representative life cycles.

Life cycle

Excepting a few, most tapeworms are digenetic, which means completing the adult stage and sexual reproduction in the primary host and the larval stage in secondary host.

The break-off gravid proglottids of the adults contain thousands of fertilized eggs with onchosphere. On reaching the ground, the proglottids eventually disintegrate and eggs are set free.

The secondary hosts become infected on consuming food contaminated with the onchosphere. In the stomach of the secondary host, the eggs lose their protective sheath due to the proteolytic enzymes and the hooked hexacanth embryo hatch out. Hexacanths embryo pierce the mucosa of the intestine to enter the blood stream and make a voyage through different organs of the body, finally landing in the striped muscle of the host. They settle there to develop into larval forms (cistycercus, hydatid cyst, coenurus, cysticercoid larvae, etc).

Feeding on such infected organs leads to the entry of the parasite into the primary host. In the small intestine, develop scolex, and transform into miniatures of the adult tapeworm. With the help of scolex, they remains attach to the intestinal mucosa in between the villi and repeat the cycle.

Fig. 6.5. Life cycle of tapeworms. Hymenolepsis nana, H. diminuta, Taenia saginata, T solium, Diphyllobothrium latum, Dipylidium craninum.

Note hexacanth embryos. Cysticercus larva in cow and pig; procercoid larva in copepod, plerocercoid (sparganum) larva in fish; cysticercoid larva in insect.

Materials

Biological samples

Movies

Mode of work

Flotation method

Direct smear

Essentially the end of the paper outlined the general characteristics of Platyhelminthes:

The phylum Platyhelminthes includes flatworms. Some are free living others are parasites.

In these animals tissue grade organization is seen i.e. the body cells aggregate into definite tissues and the tissues make up organs.

These are dorsoventrally flattened, vermiform soft bodied animals.

They exhibit bilateral symmetry with definite polarity of anterior and posterior ends.

These are triploblastic animals i.e. the body is derived from three embryonic germ layers.

A true metameric segmentation is absent.

The body is covered with a soft ciliated epidermis in the free living forms. It is covered with a cuticle in the parasitic forms.

The space between the digestive system and the body wall is filled with a connective tissue called the parenchyma. Hence there is no body cavity. Such animals are called the acoelomate animals.

Digestive canal may be well developed or poorly developed or absent. A mouth is present where there is digestive canal. Anus is absent.

Circulator, respiratory and skeleton systems are absent.

Muscular system of mesodermal origin with longitudinal, circular and oblique muscle layers are seen beneath the epidermis.

Nervous system is of primitive type and consists of a pair of anterior ganglia with longitudinal nerve cords connected by transverse nerves.

These animals have simple sense organs and they are chemo, tango and photo-receptors in the free living forms.

The excretory system consists of a lowly organized protonephridial system consisting of flame cells.

These are hermaphrodites or monoecious with complex reproductive system; well developed gonads, gonoducts and accessory organs.

There is a vitellarium and germanarium in the female reproductive system. Germarium produces the ova and the vitellarium produces the yolk material.

Fertilization is internal and life history is usually complicated with larval stages.

There may be one or two intermediate hosts for parasitic forms.

Ecobiology of nematodes (roudworms)

General Information

The nematodes or roundworms are traditionally regarded as the phylum Nematoda or Nemathelminthes.

The word Nematoda comes from the Greek words nematos, meaning thread, and eidos, meaning form, their name implies, is round rather than flat.

In contrast to platyhelminths, nematodes are cylindrical rather than flattened; hence the common name roundworm.

The nematodes may inhabit soil, fresh- and saltwater habitats, and are frequently encountered as parasites of plants, humans or animals (fig. 7.1). In general they are dioecius and in many species clear sexual dimorphism exists.

Fig. 7.1. Nematodes parasites in small intestine

Males are usually smaller than females; both may have copulatory organs.

As such, they would be the most diverse phylum of pseudocoelomates, and one of the most diverse of all animal phyla, but discussion is in progress to determine whether the phylum is to be split or not.

Nematodes are the most numerous multicellular animals on earth. A handful of soil will contain thousands of the microscopic worms, many of them parasites of insects, plants or animals.

Free-living species are abundant, including nematodes that feed on bacteria, fungi, and other nematodes, yet the vast majority of species encountered are poorly understood biologically.

Regarding on the number of nematode species there are more opinions. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. The total number of nematode species has been estimated to be about 1 million. Other sources indicate that there are nearly 20,000 described species classified in the phylum Nemata. On the other hand, it has been estimated that about 16,000–17,000 nematode species have been described and that at least 40,000 species exist. Estimates of 500,000 to a million species have no 1 basis in fact. Currently there are about 2271 described genera in 256 families. About 33% of all the nematode genera which have been described occur as parasites of vertebrates, equal to the percentage of genera known in marine and freshwater.

Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are ubiquitous in freshwater, marine, and terrestrial environments. Their many parasitic forms include pathogens in most plants and animals (including humans). Some nematodes can undergo cryptobiosis.

There are many thousands of individual nematodes in even a single handful of garden soil. Many nematodes are able to suspend their life processes completely when conditions become unfavorable; in these resistant states they can survive extreme dryness, heat, or cold, and then return to life when favorable conditions return. This is known as cryptobiosis – a feature shares with the rotifers.

External and internal anatomy

They have a smooth outside body wall (called cuticle), indicating that they are nonsegmented. The bilaterally symmetrical body (fig. 7.2.) of the unsegmented nematodes is covered by a typical cuticle which is formed by a hypodermis and must be shed during molt.

These worms, which are generally colorless and less than 5 cm long, occur almost anywhere and in great variety. In size they range from 0.3 mm to over 8 meters.

The largest nematode ever observed is Placentonema gigantisima, discovered in the placenta of a sperm whale. This 8 meter long nematode is said to have 32 ovaries. Other big verebrate parasites include Dioctophyma renale, the giant kidney worm (1m x 1.5 cm).

Most plant parasites are considerably smaller, usually measuring around 1 mm or less. Several Longidorus species exceed 10 mm in length.

Fig. 7.2. General aspect of nematodes

The body wall is composed of an outer cuticle that has a noncellular, chemically complex structure, a thin hypodermis, and musculature.

The cuticle in some species has longitudinal ridges called alae. The bursa, a flaplike extension of the cuticle on the posterior end of some species of male nematodes, is used to grasp the female during copulation.

Nematodes are structurally simple organisms. Unlike cnidarians and flatworms, nematodes have tubular digestive systems with openings at both ends.

Adult nematodes are comprised of approximately 1,000 somatic cells, and potentially hundreds of cells associated with the reproductive system.

Nematodes have been characterized as a tube within a tube ; referring to the alimentary canal which extends from the mouth on the anterior end, to the anus located near the tail. Nematodes possess digestive, nervous, excretory, and reproductive systems, but lack a discrete circulatory or respiratory system (fig. 7.3).

Over the years, nematodes have been classified in four different phyla, not always under the same name. There are two contending names for the phylum of nematodes.

The phrase tube-within-a-tube is a convenient way to think of nematode body structure, and also a term used to refer to a major trend in the evolution of triploblastic metazoa.

It refers to the development of a fluid-filled cavity between the outer body wall and the digestive tube. The nature of this body cavity has led to the grouping of metazoa into three grades, acoelomate, pseudocoelomate, and eucoelomate.

Nematodes are traditionally grouped as pseudocoelomates, on the basis of possessing a body cavity that is not formed from the mesoderm or fully lined by peritoneum. However, there are some problems in applying this concept to nematodes.

Roundworms possess two anatomical features not seen in more primitive animals: a tube-within-a-tube body plan and a body cavity.

The body cavity is a pseudocoelom, or a cavity incompletely lined with mesoderm. This fluid-filled pseudocoelom provides space for the development of organs, and serves as a type of skeleton. When roundworms are analyzed according to Table 01, they are seen to have features associated with advanced animals except that they are nonsegmented.

Fig. 7.3. Morphostructural aspect of nematodes on longitudinal and transversal sections

The cellular hypodermis bulges into the body cavity (fig. 7.3) or pseudocoelom to form four longitudinal cords—a dorsal, a ventral, and two lateral cords—which may be seen on the surface as lateral lines. Nuclei of the hypodermis are located in the region of the cords. The somatic musculature lying beneath the hypodermis is a single layer of smooth muscle cells. When viewed in cross-section, this layer can be seen to be separated into four zones by the hypodermal cords.

The musculature is innervated by extensions of muscle cells to nerve trunks running anteriorly and posteriorly from ganglion cells that ring the midportion of the esophagus.

The space between the muscle layer and viscera is the pseudocoelom, which lacks a mesothelium lining. This cavity contains fluid and two to six fixed cells (celomocytes) which are usually associated with the longitudinal cords. The function of these cells is unknown.

The Digestive System

Food of various kinds (blood, body fluid, intestinal contents, mucus etc.) is taken up by means of the species-specific mouth.

The alimentary canal of roundworms is complete, with both mouth and anus (fig. 7.4, 7.5, 7.6).

Fig. 7.4. Mouth of nematodes

Fig. 7.5. Anterior end of digestive system

Fig. 7.6. Posterior end (anus) of digestive system

The mouth is surrounded by lips bearing sensory papillae (bristles).

The esophagus, a conspicuous feature of nematodes, is a muscular structure that pumps food into the intestine; it differs in shape in different species.

The intestine is a tubular structure composed of a single layer of columnar cells possessing prominent microvilli on their luminal surface.

The nematode digestive system is generally divided into three parts, the stomodeum, intestine, and proctodeum.

The stomodeum consists of the “mouth and lips”, buccal cavity, and the pharynx (esophagus). Each of these regions is used extensively in taxonomy and classification of nematodes, as well as providing as indication of feeding habit or trophic group. For example, the buccal cavity of plant parasitic nematodes (and some insect parasites) is modified in the form of a hollow spear, adapted to penetrate and withdraw the contents of host cells. Predaceous nematodes often have a buccal cavity characterized by teeth or hook-like projections. The buccal cavity of bacterial feeding nematodes is relatively unadorned.

Bacterial feeding nematodes have the least modified or diversified stomodoeum structures. The basic plan is a circular opening surrounded by six ‘lips’, sometimes fused into three or less ‘lips’. The structures called ‘lips’ are actually cuticularly lined area of the mouth that are exposed to the outside. This opens into the buccal cavity, a triangular or cylindrical tube that can contain small ‘teeth’. Muscles extending from the body wall to the cuticular lining expand the lumen and suck food through the mouth into the buccal cavity. The buccal cavity terminates in a valve-like glottoid apparatus leading to the pharynx, also referred to as the oesophagus.

The excretory system of some nematodes consists of an excretory gland and a pore located ventrally in the mid-esophageal region. In other nematodes this structure is drawn into extensions that give rise to the more complex tubular excretory system, which is usually H-shaped, with two anterior limbs and two posterior limbs located in the lateral cords. The gland cells and tubes are thought to serve as absorptive bodies, collecting wastes from the pseudocoelom, and to function in osmoregulation (fig. 7.7, 7.8).

The excretory system, if present, empties through an anterior, ventromedial porus.

Fig. 7.7. Excretory system of nematodes

Fig. 7.8. Excretory pore of nematodes

The Nervous system

Nematodes have a nervous system that consits of two nerves that run laterally one dorsal and one ventral. Both nerves connect to a nerve ring near the base of the pharynx. Unlike most animals, nematode nerves do not split toward the muscles but the muscles stretch to the nerves (fig. 7.9).

Fig. 7.9. Nervous system of nematodes

Respiratory and circulatory systems are lacking; movements are brought about by contractions of the typically longitudinally oriented muscle cells (Fig. 8 C, D), with the fluid of the pseudocoel and the pressure of the cuticle working together as a hydrostatic skeleton.

The Reproductive System

Nematodes are in general dioecious animals (bisexual); relatively few species are hermaphrodites and, in those that are, the female and male gonads are formed consecutively.

Males are usually smaller than females, have a curved posterior end, and possess (in some species) copulatory structures, such as spicules (usually two), a bursa, or both (fig. 7.10, 7.11, 7.12).

The males have one or (in a few cases) two testes, which lie at the free end of a convoluted or recurved tube leading into a seminal vesicle and eventually into the cloaca.

Fig. 7.10. Posterior end of male

The female system is tubular also, and usually is made up of reflexed ovaries. Each ovary is continuous, with an oviduct and tubular uterus. The uteri join to form the vagina, which in turn opens to the exterior through the vulva (fig. 7.13).

Fig. 7.13. Vulvar region of nematodes

Copulation between a female and a male nematode is necessary for fertilization except in the genus Strongyloides, in which parthenogenetic development occurs (i.e., the development of an unfertilized egg into a new individual).

Some evidence indicates that sex attractants (pheromones) play a role in heterosexual mating. During copulation, sperm is transferred into the vulva of the female. The sperm enters the ovum and a fertilization membrane is secreted by the zygote. This membrane gradually thickens to form the chitinous shell. A second membrane, below the shell, makes the egg impervious to essentially all substances except carbon dioxide and oxygen. In some species, a third proteinaceous membrane is secreted as the egg passes down the uterus by the uterine wall and is deposited outside the shell.

Most nematodes that are parasitic in humans lay eggs that, when voided, contain either an uncleaved zygote, a group of blastomeres, or a completely formed larva.

Some nematodes, such as the filariae and Trichinella spiralis, produce larvae that are deposited in host tissues.

While there is much diversity represented in the reproductive structures of the Phylum Nemata, there are many features that are typical of the phylum.

Male nematodes are usually smaller than their female counterparts.

Basic male reproductive structures include: one testis, a seminal vesicle and a vas deferens opening into a cloaca.

One testis is most common, but two testes are found in some species, while in others one testis is reduced.

Spermatogonia are produced in the testis and stored in the seminal vesicle until the nematode mates.

The presences of one or two copulatory spicules help dialate the vulva and can also serve as a canal for the spermatozoa. The spicules are made from hardened cuticle, terminating in sensory dendrites near the tip.

Often the body wall around the cloaca is modified into a bursa, which helps orient the male nematode and then helps hold the two nematodes together.

Spermatozoa are amaeboid, and can have many different modifications. Some spermatozoa are round to ovoid in shape while others bear a resemblance to flagellated sperm. Different types of spermatozoa characterize different taxonomic groups of nematodes.

Basic female structures include: one or two ovaries, seminal receptacles, uteri, ovijector and a vulva. The ovary produces oogonia, which later develop into oocytes.

The seminal receptacles, sometimes developed into a spermathecea, stores the spermatozoa until they are needed to fertilize an ooctye.

The fertilized oocyte then develops into an egg in the uterus. The uteri often end in an ovijector.

The ovijector is very muscular and uses body movement combined with the high internal body pressure of the nematode to expel the egg through the vagina. Syngamy, or cross fertilization, is common in most nematodes. Hermaphroditism also occurs, with the nematode gonads producing spermatozoa first and storing them until the eggs are produced. Parthenogenesis is also a normal means of reproduction in some nematodes.

The developmental process in nematodes involves egg, larval, and adult stages. Each of four larval stages is followed by a molt in which the cuticle is shed. The larvae are called second-stage larvae after the first molt, and so on. The nematode formed at the fifth stage is the adult.

Nematode life cycles vary depending on class (fig. 7.14, 7.15). For the majority of nematodes their life cycle is a six stage process; egg, 4 larvae stages, and adult. After hatching, the larvae have about the same number of cells as an adult. Nematodes tend to grow by cell enlargement forcing the nematode to molt four times during adolescence. Once the nematode has reached adulthood it is able to reproduce. Nematodes are capable of cryptobiosis, or suspending their lives when conditions are unfavorable. Nematode life expectancy varies greatly depending on class, but generally between 20-125 days.

Fig. 7.14. General life cycle of nematodes

Fig. 7.15. Life cycles of nematodes with facultative or obligate intermediate hosts.

A Stephanurus dentatus, adults (male 2±3 cm, female 3±4.5 cm) live in cysts of kidneys of swine (final host). B Porrocaecum ensicaudatum (female 4±5 cm) live as adults in the small intestine of blackbirds. C Syngamus trachea (= redworm, gapeworm); males (6 mm) and females (20 mm) suck blood in the trachea of poultry and are permanently attached to each other, thus giving a Y-shape to the pair. 1 Eggs are mainly passed in urine (S. dentatus) or feces (other species) of final hosts. 2 On the soil the eggs embryonate, leading to a first stage larva (L1). In S. trachea development proceeds until the L3 is formed inside the egg, whereas in S. dentatus the L1 may leave the egg (2.1±2.2). Intermediate hosts may ingest the eggs (in P. ensicaudatum it is obligatory), thus initiating the development of infectious larvae (L3), which may become accumulated in considerable numbers. 3 Infection of the final hosts always occurs via the oral route. This can be: directly by ingestion of eggs containing a third-stage larva (S. trachea) or by uptake of free third-stage larvae (S. dentatus) with contaminated food; or indirectly by ingestion of intermediate hosts containing infectious third-stage larvae (possible in all three species). BC, buccal cavity; E, esophagus; IN, intestine; SH, sheath (cuticle of first- or second-stage larva); UT, uterus.

Essentially the end of the paper outlined the general characteristics of Nemathelminthes:

The members of Nemathelminthes are pseudocoelomate, vermiform bilaterally symmetrical, unsegmented animals.

These animals are in an organ-system grade of body organization.

These are free living or parasitic worms. In free living some are aquatic and some are terrestrial.

The body is cylindrical, elongated and unsegmented and usually pointed at both ends.

The name of the phylum Nematyhelminthes is derived by their resemblance to slender threads.

Mostly small sized, some are microscopic and some a meter or more in length.

There is sexual dimorphism. Males are always smaller than females.

Body is covered by a protective cuticle. It is resistant to the action of digestive juices of the host.

The epidermal cells are without cell limits. So the nuclei are scattered in the cytoplasm. Such an epidermis is called syncytium.

The body cavity is a pseudocoel, i.e. it is not lined by coelomic epithelium.

The alimentary canal is simple, straight with a mouth, anus and specialized pharynx and without digestive glands.

Respiration and circulatory systems are absent.

Excretory system consists of protonephridia and has excretory canals. Flame cells are absent.

Nervous system consists of a nerve ring. Nerve trunks arises form the nerve ring anteriorly and posteriorly.

Sense organs occur in the form of papillae and amphids.

Sexes are separate. The hind end of the male is usually covered with a cloaca and one or two copulatory spicule. The hind end of the females is straight with anus.

Some are oviparous, some are viviparous and still others are ovovivparous.

Eggs are covered with chitinous shell and cleavage is determinate and spiral.

Life cycle exhibits great variation with or without intermediate host. There is a moulting larval stage in the life cycle.

Insecta

The Insecta are the largest group of animals with respect to the number of species (~ 773,000) and to individuals. The classification is based on the original occurrence (Pterygota) or absence (Apterygota) of wings.

Insects may act as ectoparasites when sucking blood on the surface of their hosts or may even become endoparasites when entering the skin, and the intestinal and/or respiratory tracts in a variety of hosts.

These insects are encountered:

As true intermediate or final hosts of important parasites of humans and animals

As true vectors of pathogens (including an inner production phase) such as bacteriae, rickettsiae, and viruses (e.g., fleas, body lice)

As mechanical vectors of some parasites (transporting parasitic stages via mouth parts) (e.g., Entamoeba-, Giardia cysts)

The body organization of parasitic insects is very often closely adapted for its peculiar way of life and the special needs of feeding. However, the following basic features are commonly recognized:

The body shows a clear segmentation into the head (caput), breast (thorax) and trunk (abdomen), each part consisting of several specific segments (visible from outside or not).

The chitinous exoskeleton is regularly molted during growth.

The caput, the segments of which form a strong capsule, is endowed with a pair of dorsal, segmented antennae and three pairs of ventral mouth parts (mandibles, maxillae 1 and 2), the latter being strongly adapted for their special way of feeding. In general, eyes are compound and located close to the basis of the antennae; the eyes are mostly composed of numerous single ommatidia, in rare cases (e.g., fleas) only one or a few ommatidia are present.

The thorax always consists of three segments (pro-, meso- and metathorax), which each bear ventrally a pair of legs (e.g., the name hexapoda means six feet). These legs are segmented and composed of five distinct parts (coxa, trochanter, femur, tibia and tarsus); the tarsus comprises several single segments and is equipped with species-specific holdfast systems, claws, etc.

The meso- and/or metathorax may form typical membranous wings (formed by the integument) which are moved by strong inner (mostly indirect) muscular systems. Wings, however, are reduced secondarily in some groups (e.g., fleas, bedbugs, lice).

The abdominal segments form no ventral extremities except for some specific copulatory appendages. Inside the abdomen important systems of the insects are found (gonads, heart, excretory system (Malpighian tubules, etc.).

Respiration of insect’s proceeds using a large, widely branched tracheal system reaching up to the surface of single cells.

Ecobiology of diptera (flies)

General Information

The usually ectoparasitic and only seldom endoparasitic dipteran species show the following common features, although their basic body organization is modified according to their different ways of living:

The pair of forewings is always present; the hindwings have been reduced to so-called halteres

Eyes are in general large compound ones composed of numerous ommatidia

Mouth parts are of the licking-sucking type (in true flies) or of the biting type (in blood-sucking species).

The life cycle runs as holometabolous development including apod (feetless) larvae, a nonfeeding or even immotile pupa, and dioecious adults

Larvae and adults may live as parasites, larvae in general as endoparasites, and adults as ectoparasites. With the exception of a few species (Hippoboscidae), the adult dipterans feed periodically on their hosts.

True flies are insects of the order Diptera

from the Greek di = two, and ptera = wings (fig. 8.1).

Their most obvious distinction from other orders of insects is that a typical fly possesses:

a pair of flight wings on the mesothorax

and a pair of halteres, derived from the hind wings, on the metathorax.

Fig. 8.1. Wings and halteres of fly

One of the largest and most diverse orders of insects is the true flies, Diptera.

There are many species of Diptera that are of significant veterinary importance.

Diptera affecting domestic animals range from small biting flies to larger species, wingless ectoparasites, larvae that invade animal tissue, to nonbiting flies that can be of significant nuisance concern.

Many fly-borne diseases affect domestic animals.

Myiasis is the infestation of a live human being's or other vertebrate animal's body by fly larvae that feed on its tissue (fig. 8.2).

When the attack is directed against dead or necrotic tissue, the condition is not necessarily harmful and the effects may be of value as maggot therapy.

Fig. 8.2. Anal miasis

Myiasis is the invasion of organs and/or tissues of living vertebrates by the larval stages of flies (Diptera).

It encompasses the feeding on the host’s living or dead, necrotic tissues.

A diversity of fly species is involved in myiasis.

As a form of parasitism, myiasis can cause significant harm to animals and can lead to death and in some cases to less severe effects leaving little or no tissue damage.

Overall, however, myiasis should be considered of significant importance to livestock and companion animals.

Myiasis are produced by larve some species de diptera (fig. 8.3, 8.4, 8.5), specialy from family:

Calliphoridae (Calliphora, Lucillia)

Sarcophagidae (Sarcophaga Wohlfahrtia)

Oestridae (Oestrus, Hipoderma, Gasterophilus)

Fig. 8.3. Calliphora spp.

Fig. 8.4. Sarcophaga spp.

abc

Fig. 8.5. a – Oestrus spp., b – Hipoderma spp., c – Gasterophilus spp.

Adults are small (< 2mm.) to medium sized insects (- < 10mm.), larger Diptera are rare, only certain families of Diptera Mydidae and Pantophthalmidae reach 95–100 mm wingspan while tropical species of Tipulidae have been recorded at over 100 millimetres.

They have dull or bright colors, uniform or variegated and are sometimes mimetic such as in Syrphidae .

As all insects, a fly is divided into three parts: the head, thorax and abdomen (fig. 8.6, 8.7):

Head

Eyes

Antenae

Bucal apparatus

Thorax

Legs

Wings

Abdomen

Segments

Fig. 8.6. General morphology of flies. I: head; II: thorax; III: abdomen.

1: prescutum; 2: anterior stigma; 3: scutum; 4: basalare?; 5: calyptra; 6: scutellum; 7: alary nerve(costa); 8: ala; 9: urite; 10: haltere; 11: posterior stigma ; 12: femora; 13: tibia; 14: spur; 15: tarsus; 16: propleura; 17: prosternum; 18: mesopleura; 19: mesosternum; 20: metapleura; 21: metasternum; 22: compound eye; 23: arista; 24: antenna; 25: maxillary palpi ; 26: labrum (inferiore); 27: labellum; 28: pseudotrachae.

Fig. 8.7. General aspect of Calliphora.

Head

The head is distinct from the thorax , with a marked narrowing at the neck (fig. 8.8).

In "lower flies" (Nematocera), it is prognathous (head horizontally oriented with the mouth anterior), in "higher flies" (Brachycera) it is hypognathous (head vertically oriented with the mouth ventrad).

The shape of the cranial capsule also varies. In the Nematocera, the dorsal-ventral part of the head extends forward from the eyes due to the development in length of the clypeus and subgenal area subgena, the distal end of the extension is the 'mouthparts.

Fig. 8.8. General aspect of flies head.

In the "higher" Diptera the head has a subglobose shape and the fronto-clypeus is an area bounded superiorly by the eyes and the vertex.

In Cyclorrhapha Schizophora , a morphological element of particular importance is the presence of the ptilinal suture formed by the resorption of the ptilinum after emergence from the pupa.

The suture separates two regions:

1. the upper one is the frontal region, which has continuity with the apex, the orbital region and the gena;

2. the lower one, the face or clypeus, contains the insertion of the antennae and ends with the edge epistomale in at which comprises the upper lip .

The eyes are usually very obvious, but reached a remarkable development in the Brachycera. In this suborder the eyes are markedly convex and have grown to occupy most of the side of the head. The space between the two eyes can sometimes be reduced to a narrow strip running from the front of the occipital region, or disappear altogether because of the direct contact between the eyes or their margins (fig. 8.8).

The morphology of the compound eye is characterized by a significant number of ommatidia, of the order of thousands in Muscoids. The ocelli, when present, are located in the top of the head, arranged at the corners of a triangle in an area called stemmaticum or ocellar triangle.

The antennae are divided into two basic morphological types that are the basis of the distinction between the two suborders and their denomination.

In Nematocera are pluriarticulate, threadlike or of feathery type, composed of 7-15 undifferentiated items.

In Brachycera the antennae consist of up to six items, of which the first three are well-developed. In most of the families, the third segment is enlarged and the more apical segments are reduced to an appendage—called a stylus when rigid and an arista when bristle-like (fig. 8.9).

Fig. 8.9. The antennae of flies

The mouthparts show, according to the systematic group, a variety of conformations.

Mouthparts are modified and combined into a sucking proboscis, which is highly variable in structure (fig. 8.10).

The ancestral condition is the piercing and sucking type proboscis, more modified proboscis forms variously rasp or sponge fluids.

Some species have non-functional adult mouthparts.

No flies bite in the sense of cutting food.

Fig. 8.10. The mouthparts of flies

Thorax

The fundamental peculiarity of the Diptera is the remarkable evolutionary specialization achieved in the shape of the wings and the morpho-anatomical adaptation of the thorax.

Except for infrequent wingless forms the Diptera are usually winged and use the wings as the principal means of locomotion.

The level of specialization – anatomical, functional and morphological is such that in general these insects fly, often exceptionally, well, with particular reference to agility.

All Diptera are equipped with only one pair of functional wings, these are on the mesothorax (front).

The wings on the metathorax are transformed into the halteres or rocker arms.

From this characteristic comes the name of the order, from the Greek "Dipteros" which means "two wings". In consequence of this morphological structure, the mesothorax represents the segment of greater development and complexity, while the prothorax and metathorax. Are considerably reduced.

The halteres are club-shaped organs, used to balance the insect in flight, consisting of a proximal portion connected to a mechanosensory organ.

The homology between the wings and halteres is demonstrated by the four-winged mutant of the fruit fly Drosophila melanogaster.

The development of the halteres varies according to the systematic group: in the Tipulidae are they are thin but long and clearly visible, but are usually hidden by the wings in most other groups. In Calyptratae which includes the most advanced Diptera, the halteres are protected by calyptrae (small membranes above the halteres).

The morphology of the abdomen is substantially determined by morphoanatomic adaptation, in both sexes, as a function of the reproduction.

In general, the 10 urites are reduced to a lower number of urites because of structural modifications of the first urite and the last.

Tergites and sternites can be well distinguished from each other, but often there is a differential development the tergites overlaps the sternites; the extreme case is when the expansions of tergite ventrally merge, forming a tube structure or ring.

In females, the last urites become thinner and stretch forming a flexible telescopic ovipositor.

This morphological adaptation is often accompanied by sclerotisation of the terminal eighth urite, so that the ovipositor is able to penetrate through the tissues of the organism which will accommodate the eggs and larvae.

In the male, the last urites undergo a complex transformation to form a device, integrated with the genitalia called the hypopygium.

The degree and nature of structural change varies according to the systematic group, but usually involves the development of the lobes of the ninth urotergite into forceps (epandrium) and IX urosterno (hypandrium).

There is sometimes a twist along the axis of the abdomen, resulting in reversal of the positions of the epandrium and the hypandrium.

The other group of appendages are the legs. As in all insects, each leg is made up of five segments: the coxa, trochanter, femur, tibia and tarsus. There are three pairs of legs, and each segment of each pair has some structure to distinguish it from the rest.

Digestive system

The insect's digestive system is a closed system, with one long enclosed coiled tube called the alimentary canal which runs lengthwise through the body. The alimentary canal only allows food to enter the mouth, and then gets processed as it travels toward the anus. The insect’s alimentary canal has specific sections for grinding and food storage, enzyme production and nutrientabsorption. Sphincters control the food and fluid movement between three regions.

The asymmetrical tube-like gut of adult insects is oriented through the midregion of the body and consists of three main portions

stomodeum (foregut),

ventriculus (midgut),

proctodeum (hindgut).

In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax (adjacent to the fore-gut). The salivary glands (30) produce saliva, the salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium behind the hypopharynx; which movements of the mouthparts help mix saliva with food in the buccal cavity. Saliva mixes with food which travels through salivary tubes into the mouth, beginning the process of breaking it down.

Respiratory system

Insect respiration is accomplished without lungs using a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need oxygen and eliminate carbon dioxide via their cells.

Air is taken in through spiracles, openings which are positioned laterally in the pleural wall, usually a pair on the anterior margin of the meso and meta thorax, and pairs on each of the eight or less abdominal segments, Numbers of spiracles vary from 1 to 10 pairs. The oxygen passes through the tracheae to the trachioles, and enters the body by the process of diffusion. Carbon dioxide leaves the body by the same process.

Nervous system

Insects have a complex nervous system which incorporates a variety of internal physiological information as well as external sensory information. Like invertebrates the basic component is the neuron or nerve cell. This is made up of a dendrite with two projections that receive stimuli and an axon, which transmits information to another neuron or organ, like amuscle. As for vertebrates, chemicals (neurotransmitters such as acetylcholine and dopamine) are released at synapses

An insect’s sensory, motor and physiological processes are controlled by the central nervous system along with the endocrine system. Being the principal division of the nervous system, it consists of a brain, a ventral nerve cord and a subesophageal ganglion. This is connected to the brain by two nerves, extending around each side of the oesophagus.

Peripheral nervous system consists of motor neuron axons that branch out to the muscles from the ganglia of the central nervous system, parts of the sympathetic nervous system and the sensory neurons of the cuticular sense organs that receive chemical, thermal, mechanical or visual stimuli from the insects environment. The sympathetic nervous system includes nerves and the ganglia that innervate the gut both posteriorly and anteriorly, some endocrine organs, the spiracles of the tracheal system and the reproductive organs.

Sensory organs

Chemical senses include the use of chemoreceptors, related to taste and smell, affecting mating, habitat selection, feeding and parasite-host relationships. Taste is usually located on the mouthparts of the insect but in some insects, such as bees, wasps and ants, taste organs can also be found on the antennae. Taste organs can also be found on his tarsi of moths, butterfliesand flies.

Olfactory sensilla enable insects to smell and are usually found in the antennae. Chemoreceptor sensitivity related to smell in some substances is very high and some insects can detect particular odours that are at low concentrations miles from their original source.

Mechanical senses provide the insect with information that may direct orientation, general movement, and flight from enemies, reproduction and feeding and are elicited from the sense organs that are sensitive to mechanical stimuli such as pressure, touch and vibration. Hairs (setae) on the cuticle are responsible for this as they are sensitive to vibration touch and sound.

Hearing structures or tympanal organs are located on different body parts such as, wings, abdomen, legs and antennae.

The compound eye and the ocelli supply insect vision. The compound eye consists of individual light receptive units called ommatidia. Some ants may have only one or two; however dragonflies may have over 10,000. The more ommatidia the greater the visual acuity. These units have a clear lens system and light sensitive retina cells. By day, the image flying insects receive is made up of a mosaic of specks of differing light intensity from all the different ommatidia. At night or dusk, visual acuity is sacrificed for light sensitivity. The ocelli are unable to form focussed images but are sensitive mainly, to differences in light intensity. Colour vision occurs in all orders of insects. Generally insects see better at the blue end of the spectrum than at the red end. In some orders sensitivity ranges can include ultraviolet.

A number of insects have temperature and humidity sensors and insects being small, cool more quickly than larger animals. Insects are generally considered cold-blooded orectothermic, their body temperature rising and falling with the environment. However, flying insects raise their body temperature through the action of flight, above environmental temperatures.

Circulatory system

Insect blood or haemolymph’s main function is that of transport and it bathes the insect’s body organs. Making up usually less than 25% of an insect’s body weight, it transports hormones, nutrients and wastes and has a role in, osmoregulation, temperature control, immunity, storage (water, carbohydrates and fats) and skeletal function. It also plays an essential part in the moulting process.

Haemolymph contains molecules, ions and cells. Regulating chemical exchanges between tissues, haemolymph is encased in the insect body cavity or haemocoel. It is transported around the body by combined heart (posterior) and aorta (anterior) pulsations which are located dorsally just under the surface of the body. It differs from vertebrate blood in that it doesn’t contain any red blood cells and therefore is without high oxygen carrying capacity, and is more similar to lymph found in vertebrates.

Body fluids enter through one way valved ostia which are openings situated along the length of the combined aorta and heart organ. Pumping of the haemolymph occurs by waves of peristaltic contraction, originating at the body's posterior end, pumping forwards into the dorsal vessel, out via the aorta and then into the head where it flows out into the haemocoel. The haemolymph is circulated to the appendages unidirectionally with the aid of muscular pumps or accessory pulsatile organs which are usually found at the base of theantennae or wings and sometimes in the legs. Pumping rate accelerates due to periods of increased activity. Movement of haemolymph is particularly important for thermoregulation in orders such as Odonata, Lepidoptera, Hymenoptera and Diptera.

Excretory System

In insects the Malpighian tubules are of ectodermal origin and function as the main excretory system; they are blind-ending, tube-like appendages of the intestine and open at the border between the midand hindgut apparently the waste-containing hemolymph circulates in the hemocoel near these structures, the number of which is species specific

The main function is the absorption of uric acid (as sodium and potassiumsalts) and their discharge into the lumen of the intestine, from where the excretory products are passed with the feces. Strict water resorption usually occurs at the base of the Malpighian tubules and in the rectum, avoiding the waste of water.

Reproduction and development

Most parasitic insects are oviparous. In some genera (e.g., Oestrus, Sarcophaga) eggs are retained until larvae are ready for hatching (ovoviviparous).

A few species (e.g., some Musca spp., Glossina spp.) are larviparous, laying more or less highly developed larval instars. Even pupiparity can be found (e.g., Melophagus ovinus) when immobile, fully developed larval instars pupate during deposition. The ontogeny of parasiticinsects occurs either as hemimetabolous development holometabolous development.

The genitalia of female flies are rotated to a varying degree from the position found in other insects.

In some flies, this is a temporary rotation during mating, but in others, it is a permanent torsion of the organs that occurs during the pupal stage.

This torsion may lead to the anus being located below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut, despite the external organs being in their usual position

Fig. 8.11. Sexual reproduction of flies

Female

The female insect’s main reproductive function is to produce eggs, including the egg’s protective coating, and to store the male spermatozoa until egg fertilisation is ready. The female reproductive organs include, paired ovaries which empty their eggs (oocytes) via the calyces into lateral oviducts, joining to form the common oviduct. The opening (gonopore) of the common oviduct is concealed in a cavity called the genital chamber and this serves as a copulatory pouch (bursa copulatrix) when mating. The external opening to this is the vulva. Often in insects the vulva is narrow and the genital chamber becomes pouch or tube like and is called the vagina. Related to the vagina is a saclike structure, the spermatheca, where spermatozoa are stored ready for egg fertilisation. A secretory gland nourishes the contained spermatozoa in the vagina.

Egg development is mostly completed by the insect’s adult stage and is controlled by hormones that control the initial stages of oogenesis and yolk deposition. Most insects are oviviparous, where the young hatch after the eggs has been laid.

Insect sexual reproduction starts with sperm entry that stimulates oogenesis, meiosis occurs and the egg moves down the genital tract. Accessory glands of the female secrete an adhesive substance to attach eggs to an object and they also supply material that provides the eggs with a protective coating. Oviposition takes place via the female ovipositor.

Male

The male’s main reproductive function is to produce and store spermatozoa and provide transport to the reproductive tract of the female. Sperm development is usually completed by the time the insect reaches adulthood. The male has two testes, which contain follicles in which the spermatozoa are produced. These open separately into the sperm duct or vas deferens and this store the sperm. The vas deferentia then unite posteriorally to form a central ejaculatory duct, this opens to the outside on an aedeagus or a penis. Accessory glands secrete fluids that comprise the spermatophore. This becomes a package that surrounds and carries the spermatozoa, forming a sperm-containing capsule.

When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns round to face in the opposite direction. This force the male to lie on his back for his genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright.

This leads to flies having more reproduction abilities than most insects, and at a much quicker rate.

Flies occur in great populations due to their ability to mate effectively and in a short period of time during the mating season.

The female lays her eggs as close to the food source as possible and development is rapid, allowing the larvae to consume as much food as possible in a short period of time before transforming into adults.

The eggs hatch immediately after being laid, or the flies are ovoviviparous, with the larvae hatching inside the mother.

Larval flies have no true legs (fig. 8.12).

Some Dipteran larvae have prolegs adapted to such functions as holding onto a substrate in flowing water, holding onto host tissues, or holding prey.

The eyes and antennae of Brachyceran larvae are reduced or absent, and the abdomen also lacks appendages such as cerci.

This lack of features is an adaptation to food such as carrion, decaying detritus, or host tissues surrounding endoparasites.

Nematoceran larvae generally have visible eyes and antennae, though usually small and of limited function.

a

Fig. 8.12. Aspect of flies’ larvae (a) and pupae (b)

The pupae take various forms, and in some cases develop inside a silk cocoon. After emerging from the pupa, the adult fly rarely lives more than a few days, and serves mainly to reproduce and to disperse in search of new food sources (fig. 8.12).

Fig. 8.13. Life cycle of flies

Ecobiology of bees

Overview of Bees

There are an estimated 30,000 bee species worldwide. The vast majority of these species are solitary and do not produce honey or large nests with young, and therefore do not exhibit colony defense.

When one typically thinks of a bee, the species that typically comes to mind is the western honeybee, Apis mellifera. The genus Apis is comprised of eight species. Apis mellifera is comprised of 24 different races. The most common commercial production race is Apis mellifera ligustica, commonly referred to as Italians. This race is known for its high rate of honey production and its gentle nature, making it a favorite in apiaries, or commercial bee production facilities (fig. 9.1).

The majority of bees that one sees outside of a hive are workers (sterile females). A typical honeybee colony consists of 50,00060,000 sterile workers, 500 to 1000 drones (fertile males) and one queen, the only fertile female in the colony and mother of the entire population of the hive.

Some people confuse bees with wasps. Bees tend to be vegetarians and are generally hairy, whereas wasps tend to be carnivorous and hairless. The vast majority of BeeSpace activities center on the western honeybee, Apis mellifera.

Fig. 9.1. Honey bee,

Bee External Anatomy

Like all insects, the body of a bee consists of three regions, the head, the thorax, and the abdomen (fig. 9.2).

Fig. 9.2. Female Honey Bee Morphology. It can be identified as a female by both the number of divisions on its antenna and by its sting.A: Head, B: Thorax, C: Abdomen 1: Gena, 2: Vertex, 3: Ocelli, 4: Antenna, 5: Compound Eye, 6: Feelers, 7: Proboscis, 8: Foreleg, 9: Femur, 10: Middle Leg, 11: Tarsal Claw, 12: Tarsus, 13: Tibia, 14: Hind Leg, 15: Sternum, 16: Sting, 17: Hind Wing, 18: Forewing

The head houses two compound eyes, which are used for distance vision outside of the hive, as well as orienting the bee's flight relative to the sun. Each eye consists of 3000 to 5000 visual processing units called ommatidia. The eyes do not perceive shapes clearly but identify color well. A bee's compound eyes are receptive to ultraviolet light, but less receptive to reds. Bees recognize blue, yellow, and white and black (fig. 9.3).

Simple eyes, called ocelli, are found near the front and top of the head. Ocelli register intensity, wavelength, and duration of light. At dusk the ocelli estimate extent of approaching darkness, causing the bees to return to their hives.

Antennae receive and analyze highly volatile substances that are responsible for odor and taste. Antennae also perceive vibrations and movement of air, sounds, temperature (the 3 five terminal segments of the flagellum) and humidity (the eight terminal segments of the flagellum) (fig. 9.4).

The thorax includes the legs and the (fig. 9.5) wings. At the end of each leg are structures called tarsi, which taste what they touch (more specifically, they detect quality and concentration of different chemicals). Claws and arolia (soft pads between the paired claws of each leg) combine to provide an effortless hold on both smooth and rough surfaces.

The first (frontmost) pair of legs has a notch in its first terminal segment for cleaning antennae. The middle pair has spines on one side specialized for removal of masses of pollen brought to the hive. The third (hindmost) pair of legs each possess a pollen basket (corbicula) in which the pollen mass is kept during transportation from the flowers to the hive. The lower side of this pair of legs also possesses a row of stiff hairs, collectively called the pollen comb.

a b

Fig. 9.5. Legs – a, Pollen basket – b

Wings (fig. 9.6) of each bee species vary in their venation (vein) pattern. The slight differences in Apis mellifera wing venation can be useful in differentiating between races. The forewing is always larger than the hind wing. The front and hind wings are held together (coupled) by approximately 20 small hooks located along the front margin of the hind wing. Bee wings can beat nearly 200 times per second.

The abdomen consists of seven visible segments. The first is much narrowed and makes up the petiole (waist) of the bee, while the seventh segment of workers (sterile females) and queens includes the sting. Wax glands on the underside of worker abdomens secrete the wax that makes up the honeycomb.

The sting (fig. 9.7) is a modified ovipositor, so it is found only in females. When pushed from the end of the abdomen, it locks into position at a right angle to the base. Muscular abdominal plates then push the stinger into the flesh. The sting has a scalpelsharp point, with two serrated retractable rods (lancets) on the sides. The venom bulb is positioned at the top of the sting. It continues to pump venom 30 to 60 seconds after breaking off from the abdomen of the worker bee.

Up to half of the venom stored in the bulb consists of melittin, a chemical substance that causes pain, impacts blood vessels, and damages tissues. In response, the body of the stung organism produces histamines, which cause localized itching, redness and swelling.

Photolipase A2 and hyaluronidase contribute to the swelling and spread of the toxin. Additionally alarm pheromone is released at the time of the sting, stimulating further defensive response in the workers. Each worker dies shortly after stinging her victim because the sting and part of the digestive tract are left is left at the site of the stinging incident.

Internal anatomy (fig. 9.8)

The head is dominated by large compound eyes, sensitive antennae and a complex arrangement of mouthparts. The bee's head also houses the brain and contains several important glands.

Fig. 9.8. Internal anatomy of a bee

The thorax is primarily used in locomotion, as the attachment site for six legs and four wings. The ventral nerve cord, heart and esophagus pass through, but most of the space inside the thorax is taken up by sets of powerful flight muscles. Salivary glands are located ventrally, near the front of the thorax, connecting by a duct to the oral cavity in the head.

The abdomen protects the organs for the digestive system. Also present are the heart, venom sac, and several glands. The reproductive organs are also located in the abdomen. In a laying queen bee, the ovaries take up much of the space here, and account for the larger size of the abdomen. Among the sterile worker caste, however, these remain undeveloped.

The brain appears dominated by the optic lobes, which process the visual input from the large compound eyes. Honey bees also have excellent memory processing and learning abilities, necessary for long foraging flights away from their hives. The brain coordinates and regulates the functions of all the bodily systems. While only about 1 cubic millimeter in size, the honey bee's brain contains some of the most densely-packed neuropil tissue known in any animal brain.

The ventral nerve cord runs the length of the bee's body, connecting the brain with all the other organs and systems. Numerous ganglia along the way assist in coordinating local neural processing.

Worker bees possess a hypopharyngeal gland that produces royal jelly, or bee milk. This rich blend of proteins and vitamins is fed to all bee larvae for the first three days of their lives, after which workers and drones are fed a mixture of pollen and honey. When a female larva is fed continuously on royal jelly, she will rapidly develop into a queen bee. This nutritious diet will remain the only food that a queen will ever consume, allowing her to maintain a high level of continuous egg production.

The pharynx is the first section of the alimentary canal. Strong muscles here provide suction to draw in nectar from flowers. This is also the site for taste reception in insects.

The bee's esophagus is little more than a thin tube connecting the pharynx and crop. Their diet of honey and pollen does not require a powerfully musculated esophagus as in vertebrates.

The honey crop (also called the honey stomach) is where the worker bee stores collected nectar for the trip back to the hive without digesting it. A muscular valve called the proventriculus can be closed, keeping the nectar from passing into the stomach. The crop is expandable, allowing the bee to carry a larger load. Back in the hive, the contents of the crop can be ejected back through the mouth for storage in a honey cell or to feed other bees by trophallaxis.

The true stomach (or ventriculus) is the site of primary digestion for pollen and nectar. Coiled around in the abdomen, it is actually about twice the length of the bee's body. The epithelial cells that line the stomach wall are the site of attack by the microsporidia Nosema.

The hind gut is composed of the intestine and rectum, where reusable metabolic products are reclaimed and excess water is reabsorbed into the body. The rectum is also distensible, and can hold a large volume of waste matter. Bees keep meticulously clean nests, and will hold their wastes until they can make a "cleansing flight" outside of the hive. In climates with long, cold winters, bees can actually wait for weeks or months to perform this task.

Numerous Mapphigian tubules connect to the basal end of the hid gut and float freely in the abdominal cavity. They function much like the kidneys of vertebrates, removing excess salts and metabolic wastes from the blood and concentrating it into the intestine, where it can be removed.

Salivary glands are located in the front of the thorax, and connected to the mouth by a duct. This gland produces enzymes which aid in the breakdown of food. In particular, an enzyme called invertase is released, which functions to break down the sugars in nectar, and is essential to the process of converting it into honey.

An insect's heart is simply a series of musculated chambers connected the aorta, a tube that runs forward to the head. When relaxed, blood from the abdominal cavity enters the heart chambers through openings called ostioles. When it contracts, the ostioles close, and blood is forced forward through the aorta to the brain, and then circulates back through the thorax, bathing all the organs and muscle tissues along the way. This type of open circulatory system is well well-suited for a small insect.

Connected to the stinger is a venom sac, which holds a mixture of protein chemicals (the venom) and alarm chemicals. These proteins can quickly cause a painful localized reaction in vertebrates, which can be severe to life-threatening in highly sensitive individuals. When a bee stings, the barbed shaft of the stinger is left behind, along with the venom sac. An attached muscle continues to pump venom through the stinger, even after it has been disconnected from the bee. For this reason, a bee stinger should be removed immediately by scraping it with a credit card or pocket knife blade, and not by pinching it, which can forcibly inject the venom into the skin.

The antennae are important sensory organs for the bee, which must remain clean in order to function effectively. Each of bee's front legs is equipped with an antenna cleaner. This specialized notch is lined with numerous fine, stiff setae. As the shaft of the antenna is drawn through, debris is removed. The tibial spur on the front legs helps to hold the antenna against the notch.

The tibial spur of the middle legs can be used to stab the fresh wax flakes secreted by glands on the lower abdomen. The wax can then be transferred to the mandibles where it is be shaped and positioned on the comb.

The pollen press is located just below the pollen basket on the hind legs. As pollen is combed from the rest of its body, the bee uses this leg joint to compress the grains into a dense mass, which can be more efficiently stored in the corbicula

Bee Life Stages

Typical of the most advanced insects, bees exhibit complete development or complete metamorphosis. This means that the young and the adults look very different and the diet of the young and the adults typically differ, preventing the parents from competing with their offspring for resources. The life stages are egg, larva, pupa and adult. Development from egg to new worker typically takes two to three weeks.

Egg

The eggs are sometimes described as having an appearance similar to sausageshaped poppy seeds. Each egg has a small opening at the broad end of the egg, the micropyle, that allows for passage of sperm. Hatching takes place three days after egg laying.

Larva

The larval stage lasts eight to nine days. Upon hatching, the larva is almost microscopic, resembling a small, white, curved, segmented worm lacking legs and eyes. For the first two days, all larvae are fed a diet of royal jelly. Beginning the third day, worker larvae are fed honey, pollen and water, while the larvae destined to become queens continue to receive royal jelly throughout their larval lives. Regardless of whether the larva is male or female, it molts five times during its larval stage.

Care of the larvae is constant. Each larva receives an estimated 10,000 meals during this stage. Larval weight increases 5 1/2x during the first day, 1500x in six days.

Larval stage durations vary: 5.5 days for queens (fertile females), 6 days for workers (sterile females), and 6.5 days for drones (fertile males).

Pupa

The pupal stage is a stage of massive reorganization of tissues. Organs undergo a complete reorganization, while body changes from the wormlike larval body shape to the adult body shape with three distinct body regions. Pupation periods vary: queens require up to 7.5 days, drones require14.5 days, while workers require 12 days.

Adult

Adult bees are either workers (sterile females), queens (fertile females), or drones (fertile males). A typical honeybee colony consists of 50,000 60,000 sterile workers, 500 to 1000 drones (fertile males) and one queen, the only fertile female in the colony and mother of the entire population of the hive (fig. 9.9).

Fig. 9.9. Adult bees

Workers provide virtually all of the efforts required to maintain function within a hive. During the latter part of their life, each will travel up to two miles in search of pollen, nectar and water. Each worker typically goes on ten food gathering journeys per day, each lasting approximately one hour. This heavy workload takes its toll; Each worker lives for about a month prior to wearing out.

Immediately after emerging from its pupal cocoon within one of the many brood cells, it immediately goes to work. During the first four days of its adult life, each worker is cleaned and fed by the other bees while its body hardens and it begins to produce substances in various glands. Activities during the next seventeen days include cleaning, feeding larvae, manipulating wax, processing honey, guard duty and air conditioning the hive by fanning. Any of these activities can be done at any time based on the needs of the colony.

On day 21 the worker leaves the hive, and works for another 20 days, bringing in pollen, nectar, water, and propolis before taking its final flight away from the hive and dying.

Pollen, a plant protein source for the young, provides nitrogen, phosphorus, amino acids, and vitamins essential for development of these vegetarians. Pollen is collected in pollen baskets (corbicula) on the workers' rear legs.

Fig. 9.10. Tail wagging dance of heney bee workers. The straight line indicates the direction of the food sources.

Nectar, obtained from floral nectaries deep within flowers, provides a pure carbohydrate source for all stages. Each worker fills her honey sac within her digestive system, increasing her weight by up to one half. Upon arrival at the hive, the worker regurgitates the contents of the honey sac to the younger workers within the hive. These younger workers receive the nectar, which is processed by enzymes within their honey sacs, and tipped into storage cells where it ripens for five days. At this point the substance becomes honey, and the cell containing it is capped for storage. Nectar from 5 million flowers is required to produce a single pint of honey.

Water is essential for hydrating all of the individuals within a hive and cooling it throughout the year. Approximately five gallons are required to hydrate and cool the colony each year. Propolis, the final substance brought into the hive, is also called “bee glue.” It is a plant resin used to build and maintain hives.

Queens can be distinguished from workers by their longer tapered abdomens and greater size. Queens have the longest lifespan of all of the bees within the hive. Their major role centers around egg lying to insure the vast numbers of individuals required to maintain a hive.

Colonies will make a new queen if the original is ailing or infertile. This is done by producing a special wax cell around 7 or 8 fertilized eggs, the oblong armored incubator looks somewhat like a peanut. Eggs and larvae are slathered with royal jelly (vitaminrich hormonal goo made by workers) for a twoweek period, after which a new queen 10 emerges. The first new queen to emerge stings all her sisters within the specialized wax cell (all of whom are potential queens) and may kill the original queen (her mother).

Five to fifteen days after emergence from her pupal cocoon and cell, the young queen flies off, mating with as many as ten drones over a several day period. She will store the sperm from these matings in a spermatheca for the duration of her life, never to mate again.

She returns to the hive and begins laying up to 1,500 eggs per day. Queens typically lay several hundred thousand eggs over their lifetime. After two to four years, the queen uses up all of her stored sperm and begin producing unfertilized eggs, which give rise to drones. Usually the workers raise oneor more queens from the last of the fertilized eggs to replace the new queen. To maximize hive productivity, honey farmers replace the queen annually or every other year.

Drones are the male bees within a colony. Drones can be distinguished from workers and queens by their large size, rectangular abdomens, large conspicuous eyes, and noisy flight. All drones lack a sting, and have more eye facets than a worker (6,000 7,000 vs. 3,000 5,000).

Drones result from unfertilized eggs. They emerge 24 days after the egg is laid. Drones are capable of extracting honey four days after emergence, but prefer to be fed by workers. Unlike workers (sterile females), drones can't fly well, don't gather food for the colony, don't clean, don't secrete wax, and do not care for young. The role of the drones is largely to fertilize new queens. A group of drones follows each virgin queen on her early flights. Several males will mate with each virgin queen while flying, dying immediately after mating since his reproductive organs and the end of his abdomen break off, temporarily plugging the end of the queen's reproductive tract and abdomen.

Assuming all goes well; drones typically live for about 50 days. If there is a fertile female in residence, the workers may withhold food from the drones or gnaw off the drones' wings and legs. By fall, all of the males and male larvae are evicted from each colony.

A bee hive will split up into 2 or 3 new swarms each year (fig. 9.11). This is how they propagated the species. About one third of the swarm will leave the mother hive and settle in a cluster a few meters away. They sit like this while the scouts go out and find a more permanent, sheltered place to build their nest. It is at this time that that it is best to catch them so that they can be taken to a place where they won’t be a nuisance.

Fig. 9.11. The swarming of bees.

Ecobiology of ants

Introduction

Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera.

More than 12,500 out of an estimated total of 22,000 species have been classified. They are easily identified by their elbowed antennae and a distinctive node-like structure that forms a slender waist.

Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies that may occupy large territories and consist of millions of individuals.

Larger colonies consist mostly of sterile wingless females forming castes of "workers", "soldiers", or other specialised groups. Nearly all ant colonies also have some fertile males called "drones" and one or more fertile females called "queens".

The colonies sometimes are described as superorganisms because the ants appear to operate as a unified entity, collectively working together to support the colony.

Ants have colonised almost every landmass on Earth. The only places lacking indigenous ants are Antarctica and a few remote or inhospitable islands. Ants thrive in most ecosystems and may form 15–25% of the terrestrial animal biomass. Their success in so many environments has been attributed to their social organisation and their ability to modify habitats, tap resources, and defend themselves. Their long co-evolution with other species has led to mimetic, commensal, parasitic, and mutualistic relationships.

Ant societies have division of labour, communication between individuals, and an ability to solve complex problems. These parallels with human societies have long been an inspiration and subject of study.

Taxonomy and evolution

The family Formicidae belongs to the order Hymenoptera, which also includes sawflies, bees, and wasps. Ants evolved from a lineage within the vespoid wasps.

Termites, although sometimes called white ants, are not ants. They belong to the order Isoptera. Termites are more closely related to cockroaches and mantids.

Termites are eusocial, but differ greatly in the genetics of reproduction. That their social structure is similar to that of ants is attributed to convergent evolution. Velvet ants look like large ants, but are wingless female wasps.

Distribution and diversity

Ants are found on all continents except Antarctica, and only a few large islands such as Greenland, Iceland, parts of Polynesia and the Hawaiian Islands lack native ant species. Ants occupy a wide range of ecological niches, and are able to exploit a wide range of food resources either as direct or indirect herbivores, predators, and scavengers. Most species are omnivorous generalists, but a few are specialist feeders. Their ecological dominance may be measured by their biomass and estimates in different environments suggest that they contribute 15–20% (on average and nearly 25% in the tropics) of the total terrestrial animal biomass, which exceeds that of the vertebrates.

Ants range in size from 0.75 to 52 millimetres (0.030–2.0 in), the largest species being the fossil Titanomyrma giganteum, the queen of which was 6 centimetres (2.4 in) long with a wingspan of 15 centimetres (5.9 in).

Ants vary in colour; most ants are red or black, but a few species are green and some tropical species have a metallic lustre. More than 12,000 species are currently known (with upper estimates of the potential existence of about 22,000), with the greatest diversity in the tropics.

Morphology

Ants are distinct in their morphology from other insects in having elbowed antennae, metapleural glands, and a strong constriction of their second abdominal segment into a node-like petiole.

The head, mesosoma, and metasoma are the three distinct body segments. The petiole forms a narrow waist between their mesosoma (thorax plus the first abdominal segment, which is fused to it) and gaster (abdomen less the abdominal segments in the petiole). The petiole may be formed by one or two nodes (the second alone, or the second and third abdominal segments).

Like other insects, ants have an exoskeleton, an external covering that provides a protective casing around the body and a point of attachment for muscles, in contrast to the internal skeletons of humans and other vertebrates.

Insects do not have lungs; oxygen and other gases such as carbon dioxide pass through their exoskeleton via tiny valves called spiracles. Insects also lack closed blood vessels; instead, they have a long, thin, perforated tube along the top of the body (called the "dorsal aorta") that functions like a heart, and pumps haemolymph toward the head, thus driving the circulation of the internal fluids. The nervous system consists of a ventral nerve cord that runs the length of the body, with several ganglia and branches along the way reaching into the extremities of the appendages.

Head

An ant's head contains many sensory organs. Like most insects, ants have compound eyes made from numerous tiny lenses attached together. Ant eyes are good for acute movement detection, but do not offer a high resolution image. They also have three small ocelli (simple eyes) on the top of the head that detect light levels and polarization.

Fig. 10.1. Scheme ant worker anatomy

Compared to vertebrates, most ants have poor-to-mediocre eyesight and a few subterranean species are completely blind. Some ants such as Australia's bulldog ant, however, have excellent vision and are capable of discriminating the distance and size of objects moving nearly a metre away.

Two antennae ("feelers") are attached to the head; these organs detect chemicals, air currents, and vibrations; they also are used to transmit and receive signals through touch. The head has two strong jaws, the mandibles, used to carry food, manipulate objects, construct nests, and for defence. In some species a small pocket (infrabuccal chamber) inside the mouth stores food, so it may be passed to other ants or their larvae.

Legs

All six legs are attached to the mesosoma ("thorax"). A hooked claw at the end of each leg helps ants to climb and to hang onto surfaces.

Wings

Most queens and the small number of drones in a colony (the male ants), have wings; queens shed the wings after the nuptial flight, leaving visible stubs, a distinguishing feature of queens. Wingless queens (ergatoids) and males occur in a few species, however.

Metasoma

The metasoma (the "abdomen") of the ant houses important internal organs, including those of the reproductive, respiratory (tracheae), and excretory systems. Workers of many species have their egg-laying structures modified into stings that are used for subduing prey and defending their nests.

Polymorphism

In the colonies of a few ant species, there are physical castes—workers in distinct size-classes, called minor, median, and major workers. Often the larger ants have disproportionately larger heads, and correspondingly stronger mandibles. Such individuals sometimes are called "soldier" ants because their stronger mandibles make them more effective in fighting, although they still are workers and their "duties" typically do not vary greatly from the minor or median workers.

In a few species the median workers are absent, creating a sharp divide between the minors and majors. Weaver ants, for example, have a distinct bimodal size distribution. Some other species show continuous variation in the size of workers.

The smallest and largest workers in Pheidologeton diversus show nearly a 500-fold difference in their dry-weights. Workers cannot mate; however, because of the haplodiploid sex-determination system in ants, workers of a number of species can lay unfertilised eggs that become fully fertile, haploid males.

The role of workers may change with their age and in some species, such as honeypot ants, young workers are fed until their gasters are distended, and act as living food storage vessels. These food storage workers are called repletes.

This polymorphism in morphology and behaviour of workers initially was thought to be determined by environmental factors such as nutrition and hormones that led to different developmental paths; however, genetic differences between worker castes have been noted in Acromyrmex sp.

These polymorphisms are caused by relatively small genetic changes; differences in a single gene of Solenopsis invicta can decide whether the colony will have single or multiple queens.

Development and reproduction

The life of an ant starts from an egg. If the egg is fertilised, the progeny will be female (diploid); if not, it will be male (haploid). Ants develop by complete metamorphosis with the larva stages passing through a pupal stage before emerging as an adult. The larva is largely immobile and is fed and cared for by workers.

Food is given to the larvae by trophallaxis, a process in which an ant regurgitates liquid food held in its crop. This is also how adults share food, stored in the "social stomach". Larvae may also be provided with solid food such as trophic eggs, pieces of prey, and seeds brought back by foraging workers and the larvae may even be transported directly to captured prey in some species.

The larvae grow through a series of moults and enter the pupal stage. The pupa has the appendages free and not fused to the body as in a butterfly pupa. The differentiation into queens and workers (which are both female), and different castes of workers (when they exist), is influenced in some species by the nutrition the larvae obtain. Genetic influences and the control of gene expression by the developmental environment is complex and the determination of caste continues to be a subject of research. Larvae and pupae need to be kept at fairly constant temperatures to ensure proper development, and so often, are moved around among the various brood chambers within the colony.

A new worker spends the first few days of its adult life caring for the queen and young. She then graduates to digging and other nest work, and later to defending the nest and foraging. These changes are sometimes fairly sudden, and define what are called temporal castes. An explanation for the sequence is suggested by the high casualties involved in foraging, making it an acceptable risk only for ants that are older and are likely to die soon of natural causes.

Most ant species have a system in which only the queen and breeding females have the ability to mate. Contrary to popular belief, some ant nests have multiple queens while others may exist without queens. Workers with the ability to reproduce are called "gamergates" and colonies that lack queens are then called gamergate colonies; colonies with queens are said to be queen-right. The winged male ants, called drones, emerge from pupae along with the breeding females (although some species, such as army ants, have wingless queens), and do nothing in life except eat and mate.

Most ants are univoltine, producing a new generation each year. During the species-specific breeding period, new reproductives, females and winged males leave the colony in what is called a nuptial flight. Typically, the males take flight before the females. Males then use visual cues to find a common mating ground, for example, a landmark such as a pine tree to which other males in the area converge. Males secrete a mating pheromone that females follow. Females of some species mate with just one male, but in some others they may mate with as many as ten or more different males.

Mated females then seek a suitable place to begin a colony. There, they break off their wings and begin to lay and care for eggs. The females store thesperm they obtain during their nuptial flight to selectively fertilise future eggs. The first workers to hatch are weak and smaller than later workers, but they begin to serve the colony immediately. They enlarge the nest, forage for food, and care for the other eggs. This is how new colonies start in most ant species. Species that have multiple queens may have a queen leaving the nest along with some workers to found a colony at a new site, a process akin to swarming in honeybees.

A wide range of reproductive strategies have been noted in ant species. Females of many species are known to be capable of reproducing asexually through thelytokous parthenogenesis and one species, Mycocepurus smithii, is known to be all-female.

Ant colonies can be long-lived. The queens can live for up to 30 years, and workers live from 1 to 3 years. Males, however, are more transitory, being quite short-lived and surviving for only a few weeks. Ant queens are estimated to live 100 times longer than solitary insects of a similar size.

Ants are active all year long in the tropics, but, in cooler regions, they survive the winter in a state of dormancy or inactivity. The forms of inactivity are varied and some temperate species have larvae going into the inactive state, (diapause), while in others, the adults alone pass the winter in a state of reduced activity.

Communication

Weaver ants collaborating to dismember a red ant (the two at the extremities are pulling the red ant, while the middle one cuts the red ant until it snaps)

Ants communicate with each other using pheromones, sounds, and touch. The use of pheromomes as chemical signals is more developed in ants than in other hymenopteran groups.

Like other insects, ants perceive smells with their long, thin, and mobile antennae. The paired antennae provide information about the direction and intensity of scents. Since most ants live on the ground, they use the soil surface to leave pheromone trails that may be followed by other ants. In species that forage in groups, a forager that finds food marks a trail on the way back to the colony; this trail is followed by other ants, these ants then reinforce the trail when they head back with food to the colony. When the food source is exhausted, no new trails are marked by returning ants and the scent slowly dissipates. This behaviour helps ants deal with changes in their environment. For instance, when an established path to a food source is blocked by an obstacle, the foragers leave the path to explore new routes. If an ant is successful, it leaves a new trail marking the shortest route on its return. Successful trails are followed by more ants, reinforcing better routes and gradually identifying the best path.

Ants use pheromones for more than just making trails. A crushed ant emits an alarm pheromone that sends nearby ants into an attack frenzy and attracts more ants from farther away. Several ant species even use "propaganda pheromones" to confuse enemy ants and make them fight among themselves. Pheromones are produced by a wide range of structures including Dufour's glands, poison glands and glands on the hindgut, pygidium, rectum, sternum, and hind tibia. Pheromones also are exchanged, mixed with food, and passed by trophallaxis, transferring information within the colony. This allows other ants to detect what task group (e.g., foraging or nest maintenance) to which other colony members belong. In ant species with queen castes, when the dominant queen stops producing a specific pheromone, workers begin to raise new queens in the colony.

Some ants produce sounds by stridulation, using the gaster segments and their mandibles. Sounds may be used to communicate with colony members or with other species.

Defence

Ants attack and defend themselves by biting and, in many species, by stinging, often injecting or spraying chemicals such as formic acid. Bullet ants (Paraponera), located in Central and South America, are considered to have the most painful sting of any insect, although it is usually not fatal to humans. This sting is given the highest rating on the Schmidt Sting Pain Index.

The sting of Jack jumper ants can be fatal, and an antivenom has been developed for it.

Fire ants, Solenopsis spp., are unique in having a poison sac containing piperidine alkaloids. Their stings are painful and can be dangerous to hypersensitive people.

Trap-jaw ants of the genus Odontomachus are equipped with mandibles called trap-jaws, which snap shut faster than any other predatory appendageswithin the animal kingdom.

The ants were also observed to use their jaws as a catapult to eject intruders or fling themselves backward to escape a threat. Before striking, the ant opens its mandibles extremely widely and locks them in this position by an internal mechanism. Energy is stored in a thick band of muscle and explosively released when triggered by the stimulation of sensory organs resembling hairs on the inside of the mandibles. The mandibles also permit slow and fine movements for other tasks.

A Malaysian species of ant in the Camponotus cylindricus group has enlarged mandibular glands that extend into their gaster. When disturbed, workers rupture the membrane of the gaster, causing a burst of secretions containing acetophenones and other chemicals that immobilise small insect attackers. The worker subsequently dies.

Suicidal defences by workers are also noted in a Brazilian ant, Forelius pusillus, where a small group of ants leaves the security of the nest after sealing the entrance from the outside each evening.

In addition to defence against predators, ants need to protect their colonies from pathogens. Some worker ants maintain the hygiene of the colony and their activities include undertaking or necrophory, the disposal of dead nest-mates. Oleic acid has been identified as the compound released from dead ants that triggers necrophoric behaviour in Atta mexicana while workers of Linepithema humile react to the absence of characteristic chemicals (dolichodial and iridomyrmecin) present on the cuticle of their living nestmates to trigger similar behavior.

Nests may be protected from physical threats such as flooding and overheating by elaborate nest architecture. Workers of Cataulacus muticus, an arboreal species that lives in plant hollows, respond to flooding by drinking water inside the nest, and excreting it outside. Camponotus anderseni, which nests in the cavities of wood in mangrove habitats, deals with submergence under water by switching to anaerobic respiration.

Learning

Many animals can learn behaviours by imitation, but ants may be the only group apart from mammals where interactive teaching has been observed. A knowledgeable forager of Temnothorax albipennis will lead a naive nest-mate to newly discovered food by the process of tandem running. The follower obtains knowledge through its leading tutor. The leader is acutely sensitive to the progress of the follower and slows down when the follower lags and speeds up when the follower gets too close.

Nest construction

Complex nests are built by many ant species, but other species are nomadic and do not build permanent structures. Ants may form subterranean nests or build them on trees. These nests may be found in the ground, under stones or logs, inside logs, hollow stems, or even acorns. The materials used for construction include soil and plant matter, and ants carefully select their nest sites; Temnothorax albipennis will avoid sites with dead ants, as these may indicate the presence of pests or disease. They are quick to abandon established nests at the first sign of threats.

The army ants of South America and the driver ants of Africa do not build permanent nests, but instead, alternate between nomadism and stages where the workers form a temporary nest (bivouac) from their own bodies, by holding each other together.

Weaver ant (Oecophylla spp.) workers build nests in trees by attaching leaves together, first pulling them together with bridges of workers and then inducing their larvae to produce silk as they are moved along the leaf edges. Similar forms of nest construction are seen in some species of Polyrhachis.

Some ant species build nests in and on buildings. Interior spaces in walls, windows, and even electric appliances such as clocks, lamps, and radios in the interior of buildings may be used as sites for nests.

Cultivation of food

Most ants are generalist predators, scavengers, and indirect herbivores, but a few have evolved specialised ways of obtaining nutrition. Leafcutter ants (Atta and Acromyrmex) feed exclusively on a fungus that grows only within their colonies. They continually collect leaves which are taken to the colony, cut into tiny pieces and placed in fungal gardens. Workers specialise in related tasks according to their sizes. The largest ants cut stalks, smaller workers chew the leaves and the smallest tend the fungus. Leafcutter ants are sensitive enough to recognise the reaction of the fungus to different plant material, apparently detecting chemical signals from the fungus. If a particular type of leaf is found to be toxic to the fungus, the colony will no longer collect it. The ants feed on structures produced by the fungi called, gongylidia. Symbiotic bacteria on the exterior surface of the ants produce antibiotics that kill bacteria introduced into the nest that may harm the fungi.

Navigation

Foraging ants travel distances of up to 200 metres (700 ft) from their nest and scent trails allow them to find their way back even in the dark. In hot and arid regions, day-foraging ants face death by desiccation, so the ability to find the shortest route back to the nest reduces that risk. Diurnal desert ants of the genus Cataglyphis such as the Sahara desert ant navigate by keeping track of direction as well as distance travelled. Distances travelled are measured using an internal pedometer that keeps count of the steps taken and also by evaluating the movement of objects in their visual field (optical flow). Directions are measured using the position of the sun. They integrate this information to find the shortest route back to their nest. Like all ants, they can also make use of visual landmarks when available as well as olfactory and tactile cues to navigate. Some species of ant are able to use the Earth's magnetic field for navigation. The compound eyes of ants have specialised cells that detect polarised light from the Sun, which is used to determine direction. These polarization detectors are sensitive in the ultraviolet region of the light spectrum. In some army ant species, a group of foragers who become separated from the main column sometimes may turn back on themselves and form a circular ant mill. The workers may then run around continuously until they die of exhaustion. Such wheels have been observed in other ant species, notably when a group has fallen into or been overcome with water, whereby the group rotates in a partially submerged circle on the surface of the water. The behavior could allow survival of a brief flooding.

Locomotion

The female worker ants do not have wings and reproductive females lose their wings after their mating flights in order to begin their colonies. Therefore, unlike their wasp ancestors, most ants travel by walking. Some species are capable of leaping. For example, Jerdon's jumping ant (Harpegnathos saltator) is able to jump by synchronising the action of its mid and hind pairs of legs. There are several species of gliding ant including Cephalotes atratus; this may be a common trait among most arboreal ants. Ants with this ability are able to control the direction of their descent while falling.

Other species of ants can form chains to bridge gaps over water, underground, or through spaces in vegetation. Some species also form floating rafts that help them survive floods. These rafts may also have a role in allowing ants to colonise islands. Polyrhachis sokolova, a species of ant found in Australian mangrove swamps, can swim and live in underwater nests. Since they lackgills, they go to trapped pockets of air in the submerged nests to breathe.

Cooperation and competition

Not all ants have the same kind of societies. The Australian bulldog ants are among the biggest and most basal of ants. Like virtually all ants, they areeusocial, but their social behaviour is poorly developed compared to other species. Each individual hunts alone, using her large eyes instead of chemical senses to find prey.

Some species (such as Tetramorium caespitum) attack and take over neighbouring ant colonies. Others are fewer expansionists, but just as aggressive; they invade colonies to steal eggs or larvae, which they either eat or raise as workers or slaves. Extreme specialists among these slave-raiding ants, such as the Amazon ants, are incapable of feeding themselves and need captured workers to survive. Captured workers of the enslaved speciesTemnothorax have evolved a counter strategy, destroying just the female pupae of the slave-making Protomognathus americanus, but sparing the males (who don't take part in slave-raiding as adults).

Ants identify kin and nestmates through their scent, which comes from hydrocarbon-laced secretions that coat their exoskeletons. If an ant is separated from its original colony, it will eventually lose the colony scent. Any ant that enters a colony without a matching scent will be attacked. Also, the reason why two separate colonies of ants will attack each other even if they are of the same species is because the genes responsible for pheromone production are different between them. The argentine ant, however, does not have this characteristic, due to lack of genetic diversity, and has become a global pest because of it.

Parasitic ant species enter the colonies of host ants and establish themselves as social parasites; species such as Strumigenys xenos are entirely parasitic and do not have workers, but instead, rely on the food gathered by their Strumigenys perplexa hosts. This form of parasitism is seen across many ant genera, but the parasitic ant is usually a species that is closely related to its host. A variety of methods are employed to enter the nest of the host ant. A parasitic queen may enter the host nest before the first brood has hatched, establishing herself prior to development of a colony scent. Other species use pheromones to confuse the host ants or to trick them into carrying the parasitic queen into the nest. Some simply fight their way into the nest.

A conflict between the sexes of a species is seen in some species of ants with these reproductives apparently competing to produce offspring that are as closely related to them as possible. The most extreme form involves the production of clonal offspring. An extreme of sexual conflict is seen in Wasmannia auropunctata, where the queens produce diploid daughters by thelytokous parthenogenesis and males produce clones by a process whereby a diploid egg loses its maternal contribution to produce haploid males who are clones of the father.

Relationships with other organisms

Ants form symbiotic associations with a range of species, including other ant species, other insects, plants, and fungi. They also are preyed on by many animals and even certain fungi. Some arthropod species spend part of their lives within ant nests, either preying on ants, their larvae, and eggs, consuming the food stores of the ants, or avoiding predators. These inquilines may bear a close resemblance to ants. The nature of this ant mimicry (myrmecomorphy) varies, with some cases involving Batesian mimicry, where the mimic reduces the risk of predation. Others show Wasmannian mimicry, a form of mimicry seen only in inquilines.

Aphids and other hemipteran insects secrete a sweet liquid called honeydew, when they feed on plant sap. The sugars in honeydew are a high-energy food source, which many ant species collect. In some cases, the aphids secrete the honeydew in response to ants tapping them with their antennae. The ants in turn keep predators away from the aphids and will move them from one feeding location to another. When migrating to a new area, many colonies will take the aphids with them, to ensure a continued supply of honeydew. Ants also tend mealybugs to harvest their honeydew. Mealybugs may become a serious pest of pineapples if ants are present to protect mealybugs from their natural enemies.

Myrmecophilous (ant-loving) caterpillars of the butterfly family Lycaenidae (e.g., blues, coppers, or hairstreaks) are herded by the ants, led to feeding areas in the daytime, and brought inside the ants' nest at night. The caterpillars have a gland which secretes honeydew when the ants massage them. Some caterpillars produce vibrations and sounds that are perceived by the ants. Other caterpillars have evolved from ant-loving to ant-eating: these myrmecophagous caterpillars secrete a pheromone that makes the ants act as if the caterpillar is one of their own larvae. The caterpillar is then taken into the ant nest where it feeds on the ant larvae.

Fungus-growing ants that make up the tribe Attini, including leafcutter ants, cultivate certain species of fungus in the Leucoagaricus or Leucocoprinus genera of the Agaricaceae family. In this ant-fungus mutualism, both species depend on each other for survival. The ant Allomerus decemarticulatus has evolved a three-way association with the host plant, Hirtella physophora (Chrysobalanaceae), and a sticky fungus which is used to trap their insect prey.

Lemon ants make devil's gardens by killing surrounding plants with their stings and leaving a pure patch of lemon ant trees, (Duroia hirsuta). This modification of the forest provides the ants with more nesting sites inside the stems of the Duroia trees. Although some ants obtain nectar from flowers, pollination by ants is somewhat rare. Some plants have special nectar exuding structures, extrafloral nectaries that provide food for ants, which in turn protect the plant from more damaging herbivorous insects. Species such as the bullhorn acacia (Acacia cornigera) in Central America have hollow thorns that house colonies of stinging ants (Pseudomyrmex ferruginea) that defend the tree against insects, browsing mammals, and epiphyticvines. Isotopic labelling studies suggest that plants also obtain nitrogen from the ants. In return, the ants obtain food from protein- and lipid-richBeltian bodies. Another example of this type of ectosymbiosis comes from the Macaranga tree, which has stems adapted to house colonies of Crematogaster ants.

Many tropical tree species have seeds that are dispersed by ants. Seed dispersal by ants or myrmecochory is widespread and new estimates suggest that nearly 9% of all plant species may have such ant associations. Some plants in fire-prone grassland systems are particularly dependent on ants for their survival and dispersal as the seeds are transported to safety below the ground. Many ant-dispersed seeds have special external structures, elaiosomes that are sought after by ants as food.

A convergence, possibly a form of mimicry, is seen in the eggs of stick insects. They have an edible elaiosome-like structure and are taken into the ant nest where the young hatch.

Most ants are predatory and some prey on and obtain food from other social insects including other ants. Some species specialise in preying on termites (Megaponera and Termitopone) while a few Cerapachyinae prey on other ants. Some termites, including Nasutitermes corniger, form associations with certain ant species to keep away predatory ant species. The tropical wasp Mischocyttarus drewseni coats the pedicel of its nest with an ant-repellant chemical. It is suggested that many tropical wasps may build their nests in trees and cover them to protect themselves from ants. Stingless bees (Trigona and Melipona) use chemical defences against ants.

Flies in the Old World genus Bengalia (Calliphoridae) prey on ants and are kleptoparasites, snatching prey or brood from the mandibles of adult ants. Wingless and legless females of the Malaysian phorid fly (Vestigipoda myrmolarvoidea) live in the nests of ants of the genus Aenictus and are cared for by the ants.

Fungi in the genera Cordyceps and Ophiocordyceps infect ants. Ants react to their infection by climbing up plants and sinking their mandibles into plant tissue. The fungus kills the ants, grows on their remains, and produces a fruiting body. It appears that the fungus alters the behaviour of the ant to help disperse its spores in a microhabitat that best suits the fungus. Strepsipteran parasites also manipulate their ant host to climb grass stems, to help the parasite find mates.

A nematode (Myrmeconema neotropicum) that infects canopy ants (Cephalotes atratus) causes the black-coloured gasters of workers to turn red. The parasite also alters the behaviour of the ant, causing them to carry their gasters high. The conspicuous red gasters are mistaken by birds for ripe fruits such as Hyeronima alchorneoides and eaten. The droppings of the bird are collected by other ants and fed to their young, leading to further spread of the nematode.

South American poison dart frogs in the genus Dendrobates feed mainly on ants, and the toxins in their skin may come from the ants.

Army ants forage in a wide roving column, attacking any animals in that path that are unable to escape. In Central and South America, Eciton burchelliiis the swarming ant most commonly attended by "ant-following" birds such as antbirds and woodcreepers. This behaviour was once consideredmutualistic, but later studies found the birds to be parasitic. Although direct kleptoparasitism (birds stealing food from the ants' grasp) is rare, the birds eat many prey insects that the ants would otherwise eat and thus decrease their foraging success. Birds indulge in a peculiar behaviour calledanting that, as yet, is not fully understood. Here birds rest on ant nests, or pick and drop ants onto their wings and feathers; this may be a means to remove ectoparasites from the birds.

Anteaters, aardvarks, pangolins, echidnas, and numbats have special adaptations for living on a diet of ants. These adaptations include long, sticky tongues to capture ants and strong claws to break into ant nests. Brown bears (Ursus arctos) have been found to feed on ants. About 12%, 16%, and 4% of their faecal volume in spring, summer, and autumn, respectively, is composed of ants.

Relationship with humans

Ants perform many ecological roles that are beneficial to humans, including the suppression of pest populations and aeration of the soil. The use of weaver antsin citrus cultivation in southern China is considered one of the oldest known applications of biological control. On the other hand, ants may become nuisances when they invade buildings, or cause economic losses.

In some parts of the world (mainly Africa and South America), large ants, especially army ants, are used as surgical sutures. The wound is pressed together and ants are applied along it. The ant seizes the edges of the wound in its mandibles and locks in place. The body is then cut off and the head and mandibles remain in place to close the wound.

Some ants of the family Ponerinae have toxic venom and are of medical importance. The species include Paraponera clavata (Tocandira) and Dinoponera spp. (false Tocandiras) of South America and the Myrmecia ants of Australia.

In South Africa, ants are used to help harvest rooibos (Aspalathus linearis), which are small seeds used to make a herbal tea. The plant disperses its seeds widely, making manual collection difficult. Black ants collect and store these and other seeds in their nest, where humans can gather them en masse. Up to half a pound (200 g) of seeds may be collected from one ant-heap.

Although most ants survive attempts by humans to eradicate them, a few are highly endangered. Mainly, these are island species that have evolved specialized traits. They include the critically endangered Sri Lankan relict ant (Aneuretus simoni) and Adetomyrma venatrix of Madagascar.

Ecobiology of fleas

Introduction

Fleas are wingless insects, with a laterally compressed body of about 1.5-4 mm length (fig. 11.1). The mouthparts adapted for piercing skin and sucking blood. Fleas are external parasites, living by hematophagy off the blood of mammals and birds.

Like all insects they possess six legs and three body segments. Taxonomically they belong to the order Siphonaptera, which contains several species and subspecies.

Fleas represent one of the most important ectoparasites. At the moment there are more than 2000 described species and subspecies throughout the world.

These species belong to the families Pulicidae, including Pulex spp., Ctenocephalides spp., Spilopsyllus spp. and Archaeopsyllus spp., or the familia Ceratophyllidae with the genuses Ceratophyllus or Nosopsyllus to mention only some of the most important veterinary and human representatives.

About 95% of the ~2000 different flea species parasitize on mammals, 5% live on birds.

Fig. 11.1. Adult fleas

General Morphology

The flea is dark brown in color, wingless and possesses a laterally compressed chitineous abdomen. The glossy surface of the body allows easy movement through hair and feathers. Compound eyes are absent, but some species have large or small simple eyes. The legs are long, strong and adapted for leaping. This can especially be seen in the third pair of legs which is much longer than the others and muscular (fig. 11.2).

In some species there are a number of large spines on the head and the thorax known as ‘combs’ or ctenidia. There may be a genal comb on the cheek (gena) and a pronotal comb on the posterior border of the first thoracic segment. These combs or ctenidia belong to one of the three sets of characteristics in morphological taxonomy for identifying fleas, the so-called chateotaxy.

Thoracic and leg structures and the structure of the male segment IX, the female sternite VII and the sperm holding organ (spermatheca) are the other two characterizing sets.

Fig. 11.2. Scheme flea anatomy

Developmental Cycle of Fleas

The flea develops via a number of stages, beginning with the egg, followed by the larva, pupa and finally adult stage. The life cycle of the flea is one of complete metamorphosis (fig. 11.3).

It can be completed in as little as 14 days or be prolonged up to 140 days, depending mainly on temperature and humidity. The life cycle of most flea species is characterized by three events: the hatching of the egg, the period from 1st instar to pupa, and the period from pupa to adult.

Adults of both sexes are blood-sucking parasites. Adults may live for 2 years or longer and may survive for 4-6 months without feeding. Eggs are normally laid off the host, but if they are laid on the host they soon drop to the ground, where they hatch in 2-12 days. Larvae are maggot-like in appearance with a coat of bristles. They have chewing mouthparts and feed on debris and the bloody excrement of the adults, which gives them a reddish color. They molt twice before spinning a cocoon in which the pupa develops. Under ideal conditions, the life cycle may be completed within 3 weeks; however, it may take several months or years. The pupal stage may last up to a year, depending upon the humidity and temperature. The pupae emerge in response to any vibration, thereby causing swarms of fleas.

Fig. 11.3. Life cycle of fleas.

Eggs

Flea eggs possess a widely oval form, rounded at both ends, a slightly transparent color at the beginning, later a pearly white color, 0.5 x 0.3 mm size, a smooth surface which can slightly darken later on, and they are well visible to the naked eye (Fig. 11.4).

Fig. 11.4. EM picture of a flea egg

Adult female fleas may produce from eleven to 46 eggs per day. The important egg characteristics:

Oval shape with a white shiny ivory surface

Size 5 mm in length

Appear 24 to 36 hours after first blood meal

Average 27 ova per day

Favorable condition: relative humidity >50%, temperature around 25° C

Larvae

Most flea species parasitize nest-dwelling animals, and the great majority of flea larvae live in the nest or den of their hosts. Among the nest-inhabiting flea larvae, there is a gradation of dependence on the host and on adult fleas for nutrition. In fleas, both larvae and adults are dependent on the blood of the host, and the larvae can be determined as obligate parasites.

Newly hatched flea larvae are slender, white, apod (i.e. without feet), sparsely covered with short hair, two to five millimeters in length, and posses a pair of anal struts. Their body consists furthermore of a yellow-to-brownish head three thoracal (breast) segments and ten abdominal (belly) segments. The larvae have chewing mouth parts and are free-living (fig. 11.5). As the larvae have no feet they move by using their skin muscle tube on dry surface, managing to move quite rapidly. They are only able to stop by using the mouth parts and less effectively the soft push of the last segment.

The larva of the flea furthermore passes through two molts, thus having three larval instars, and the third larval instar pupates. The first larval instar is approximately 2 mm in length, and the third instar can be 4 to 5 mm long.

The larval development occurs in protected microhabitats that combine moderate temperatures, high relative humidity and a source of nutrition in form of adult flea fecal blood

Apart from adult flea fecal blood, no organic material with the exception of flea eggs as well as injured flea larvae was proven to be ingested by cat flea larvae, this as an example of a form of cannibalism.

Outdoor survival is strongly influenced by temperature and humidity. Very high larval mortality was reported in sun-exposed areas (100%).

The important larval characteristics:

Larval hatch temperature- and humidity-dependent

Average time 1 – 10 days after egg deposit

First instar larvae 1 – 2 mm in size

Three larval stages L1 to L3 (two moults)

Third larval stage size 4 – 5 mm

Color: first white, later rust-brown

Life span 5 to 12 days

Fig. 11.5. Micrograph of a fleas larvae

Pupae

After completing development, the late third instar larva voids its alimentary canal contents in preparation of forming a cocoon and moves to an undisturbed place to spin a silk-like cocoon in which it pupates.

The principal factors triggering pupation are declining levels of juvenile insect hormone.

The silkin excretes for the cocoon is produced by the salivary glands. The resulting cocoon consists of soft and moist silk-like material, measures about 4 by 2 mm, is loosely spun and whitish in color and is coated with dust and debris because of its stickiness which aids in camouflaging it perfectly.

Flea cocoons can be found in soil, on vegetation, in carpets, under furniture, and on animal bedding.

Females develop into adults about 1.6 days faster than males.

The pupa is suggested to be the stage most likely to survive extended periods in cool dry climates.

The important pupa characteristics:

Final stage prior to adult insect emergence (insect metamorphosis)

Three stages in cocoon: U-shape prepupa,

true pupa and preemergent adult

Size approximathly 5 mm in length

Spins cocoon for protection (time to built 5 – 14 days)

Best protected and resistant life stage

Favorable condition: 27oC and relative humidity >50%

Female adults hatch before males

(Development time: 1.6 days faster than males)

Preemerged Adults

Preemerged Adults

Depending on the temperature inside the cocoon the flea develops via the stages prepupa and pupa within seven to 19 days into an adult which at first rests inside the cocoon. The observation of adult fleas remaining quiescent for prolonged periods within the pupal cocoon before emergence has been made by several researchers and characterizes the so-called preemerged adult.

The preemerged adult has a lower respiratory demand than the emerged adult and its survival is considerably longer under low humidity conditions. By that stage, prolonged adult survival within the cocoon, particularly under desiccating conditions, is possible and mainly due to quiescent periods of low metabolic activity rather than restriction of water loss through the cocoon wall. It can be suggested that the preemerged stage is ideal for prolonged survival during the absence of hosts or during unfavorable environmental conditions such as in winter or midsummer.

Pressure and heat are the two main stimuli inducing rapid emergence from the cocoon, in detail pressure of 13-254 g/cm2 and temperature between 32-38°C. Since the combination of warmth and pressure provide higher emergence rates than either warmth or pressure alone, it is likely that an endothermic animal resting on a cocoon increases the chance that the adult flea would emerge and successfully attack the host. A man with a body weight of >75 kg walking over a carpet containing cocoons induces the emergence of 31% of the cocoons’ population after the first walk, 97% after the fourth and all the imagines emerge after the fifth time. In the absence of stimuli adults emerging gradually over several weeks, depending on ambient temperature, with the length of time spent in the cocoon related to prepupal weight.

The important Preemerged Adults characteristics:

The “waiting stage”

Emergence after 10 days or 6 months (known as “the pupal window”)

Survival stage of non-parasitic-periods (no host available)

Important feature of evolution, due to coevolution with very

mobile hosts

Stimuli for rapid emergence are:

pressure (walking by a potential host)

heat (body temperature of a potential host)

Adults

Once the flea emerges from the cocoon, it will not undergo any further molts, and the only size increase occurs due to swelling of the abdomen after feeding.

After emerging from the cocoon, the flea almost immediately begins seeking a host searching for a blood meal. A variety of stimuli attract newly emerged fleas. Visual and thermal factors have been found to be primarily responsible for attraction and orientation to the host.

Fleas possess specialized, powerful legs for jumping onto a host; their jump seems to be directed but not precise, responding to the amount of stimulus and not to the pattern. Thirty-four centimeters have been recorded in jumping (fig. 11.6).

After the first blood meal, the flea must continue to feed and reproduce in order to keep its metabolism in balance. The adult flea is the perfect example of a parasite that must live on its host in order to survive. As an adult, its only function is to reproduce and it must feed constantly in order to do so.

Fig. 11.6. Adult fleas parasites in animals

Bloodfeeding is apparently necessary for oviposition as well as for successful mating. Males require feeding before the epithelial plug is unblocked in their testes.

For blood intake, the suctorial mouth parts, well adapted to piercing and sucking from the skin are used. The host’s epidermis is penetrated by the flea’s maxillae. A tube, the epipharynx, enters the capillary vessels and draws up blood while saliva from the maxillae is deposited in the surrounding tissue.

Maximum longevity of fleas has not completely been demonstrated, but survival on hosts which have been restricted in grooming activity has been reported for at least 133 days.

The important adult flea’s characteristics:

The final stage of insect metamorphosis

Distinguished stage with females and males

Host attack stimuli are: tactile stimuli, CO2, air currents and light

Unfed adults’ survival time: about 20 – 62 days

(dependent on climate)

Fed adults on host survival time: up to 133 days

Blood intake in female fleas: 13.6 μl/ day, equivalent to 15.2-times

the body weight

Start of feeding means regular blood meals necessary to survive

Economic Importance

Veterinary Importance

Flea allergy dermatitis (FAD) is one of the most frequent causes of skin conditions in pets and a major clinical entity in dogs;

The hypersensitivity to flea bites is not only seen in dogs but also a major cause of feline miliary dermatitis ;

Besides the dermal aspect, fleas as hematophagous insects can also cause an unbalance in the circulatory system. Iron deficiency anemia in heavy infestations can be particularly produced in young animals;

The last aspect of veterinary importance of flea infestations is the role as transmitter of a variety of diseases which also represent a potential health risk for humans;

Important for the host is the infection with the cestode Dipylidium caninum by ingesting infested fleas and the infection with the subcutaneous filarid nematode Dipetalonema reconditum as a non-pathogenic filarid which must be considered as differential diagnosis of the microfilariae of the pathogenic dog heartworm, Dirofilaria immitis.

Medical Importance

In general there have been risks and health problems connected with arthropods. Concerning fleas, their readiness to parasite humans as alternative hosts gives the fleas of domestic animals relevance in public health.

Ecobiology of mites

The order Acarina (class Arachnida) includes mites (fig. 12.1) and ticks. Members of this order differ from other arachnids in that the body is not segmented, and the cephalothorax and abdomen are combined into one body region.

Larval mites and ticks have three pairs of legs, whereas nymphs and adults have four pairs.

a b

Fig. 12.1. The microscopic mite Lorryia formosa – a, Oribatid mites -b

Mites comprise a very large group; scientists estimate that there may be as many as a million different types, but so far only about 50,000 have been identified and named.

Mites have very diverse biologies. Many live in the soil where they feed on microorganisms, fungi, or dead organic matter, or where they prey on other mites, small insects and even nematodes. Others occur in the water where they have similar diverse habits.

Many mites are parasitic on insects or higher animals such as birds, reptiles, and mammals.

Mites belong to the order Acarina within the phylum Arthropoda (subphylum Chelicerata), and include about 30,000 species in a worldwide distribution. While fed, ticks can reach a length of up to 30 mm, but mites are relatively small arthropods with a body length of 0.2±4 mm. In contrast to ticks, mites often possess relatively long hairs (fig. 12.1).

The anatomies of acarines, as shown in figure 12.2., are fairly similar. The capitulum is the head and the idiosoma is the body. The idiosoma is composed of the propodosoma, metapodosoma, and opisthosoma.

The segmentation that divides the propodosoma from the hysterosoma is the hallmark of Arachnida. It is important to note that in Acari there is no division between the metapodosoma (thorax) and the opisthosoma (abdomen). This makes the body rounded.

Each leg (LE) is numbered starting from the head. Adult mites have eight (four pairs of) legs versus their 6-legged insect cousins from the subphylum Hexapoda (six legs in Greek).

The top portion of the capitulum, the gnathosoma, has two additional pairs of short appendages (one of which are the chelicerae mentioned earlier) that have evolved for feeding, sensing, and reproducing. Also, they don’t have antennae or wings like insects, but they do have hair-like bristles called setae.

The shape of the body, as well as of the extremities and mouth parts, may differ considerably between the different groups of mites. In general, the chelicerae are adapted to piercing, sucking or chewing. In members of the Acarina the prosoma and opisthosoma are fused, forming a more or less rounded body (fig. 12.2).

If present, eyes are on the surface of the prosoma.

Fig. 12.2. Diagrammatic representation of the body of a typical mite. LE, leg

The exoskeleton, which contains chitin, can be more or less sclerotized; there are species with soft skin, while the body of others can be covered by sclerotized shields of different size.

Integument

The epidermis of mites secretes a cuticle which in principle is a typical arthropod cuticle, i.e., it is composed of a distinct epicuticle exhibiting sublayers (outer and inner epicuticle), a cover of secretory material of varying thickness (= cerotegument) perhaps corresponding to the cement and wax layers present in other arthropods, and the procuticle.

Intestine and Food Uptake

The intestine of mites (fig. 12.3) consists of several definite compartments.

Fig. 12.3. Diagrammatic representation of the alimentary tract and the brain of a mite

The mouth and the buccal cavity are followed by a muscular pharynx which is connected with the midgut (ventriculus) by a tubular esophagus. The midgut may be enlarged by up to seven ceca. From the ventriculus a short intestine leads to the hindgut. The last part of the alimentary tract is the rectum, which opens at the anus.

The organization of the alimentary tract can vary in the different groups of mites.

One or two pairs of Malpighian tubules may insert at the posterior intestine. Digestion proceeds both intra- and extracellularly, depending on the region of the midgut.

Excretory System

The organs involved in excretion vary between species. In most species midgut cells serve as excretory organs by absorbing excretes during digestion and discharging them later into the lumen of the ventriculus, from where they are passed with the feces.

In addition, there may be several Malpighian tubules, a single median excretory tube, and/or coxal glands. Malpighian tubules arise from the border between the midand hindgut and may be present in one or two pairs; in some species they may be reduced or even absent. Prostigmatid mites possess a median excretion tube originating from the hindgut, whereas their midgut terminates blindly. Coxal glands consist of a coelomic sac and a coiled canal which opens on or near the coxae inside a definite porus. Some excretory systems are involved in osmoregulation.

Nervous System

Mites possess a well developed central nervous system, formed by ganglia encircling the esophagus (fig. 12.3). Nerves of the subesophageal ganglia innervate musculature, legs, alimentary systems and reproductive organs. Starting from the ganglia and situated dorsally to the esophagus, nerves arise which supply the mouth parts and, if present, the eyes. There are different sensory structures on the body surface of mites. Setal receptors occur in various shapes and with different internal structures. Tactile and chemosensory setae are to be distinguished; the latter are often optically active, too. The trichobothria are a type of tactile sensory organ that is solid internally in contrast to other tactile setae.

Some mites possess ocelli, whereas in some eyeless groups photosensitive areas have been described on the dorsum.

Reproduction and Life cycle

Reproduction of mites is usually bisexual, but facultatively parthenogenesis may occur. The reproductive systems of mites are in general very similar to those of ticks.

In terms of reproduction systems, the mites are fairly sophisticated. The males have a gonopore at the end of an ejaculatory apparatus, a vas deferens, and testes. The females have ovaries, vaginas, and vaginal glands.

Three developmental stages can be distinguished: the larva with only three pairs of legs, the (mostly) two nymphal stages (protonymph, deutonymph), and the adults (all with four pairs of legs).

Medical significance

Some mites are of medical importance. Those that feed on food stocks, dust, etc. can cause allergies in humans since parts of their bodies may act as allergens if sensitive persons get into contact with the mites or inhale part of them.

Some feed on dead skin and can cause dermatitis. Other mites are harmful to men and animals by sucking body fluids (blood, lymph). During their meal the host may become infected with viruses, rickettsiae or filarial nematodes.

Digging mites such as Sarcoptes spp. produce scabies in humans and mange in animals by making funnels in the skin that become inflamed due to secondary bacterial invasion.

Some mites are parasitic on invertebrates, such as Varroa jacobsoni which can cause death of bee colonies by damaging the brood.

Dusts mites cause several forms of allergic diseases, including hay fever, asthma and eczema and are known to aggravate atopic dermatitis. Mites are usually found in warm and humid locations, including beds. It is thought that inhalation of mites during sleep exposes the human body to some antigens that eventually induce hypersensitivity reaction. Dust mite allergens are thought to be among the heaviest dust allergens.

Ecobiology of ticks

Systematic and general morphology

Ticks are small arachnids in the order Ixodida. Along with mites, they constitute the subclass Acarina. Ticks are members of the same phylum (Arthropoda) of the animal kingdom as insects, but are in a different class.

The ticks are subdivided into three families, namely the Argasidae and the Ixodidae, to which most ticks belong, and the Nuttalliellidae, which is a monotypic family, characterized by features mainly intermediate to those of the two major tick families. The two major families, the “soft” Argasidae and the “hard” Ixodidae, can be differentiated according to the following biological and behavioral criteria (fig. 13.1, 13.2).

Fig. 13.1. Hard ticks

Fig. 13.2. Soft ticks.

Approximately 850 tick species have been described worldwide. The family Ixodidae is by far the largest and economically most important family with 13 genera and approximately 650 species.

Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians.

Ticks are vectors of a number of diseases, including Lyme disease, Q fever (rare; more commonly transmitted by infected excreta), Colorado tick fever, Rocky Mountain spotted fever, African tick bite fever, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis, Tick paralysis and tick-borne meningoencephalitis, as well as bovine anaplasmosis.

Ticks are blood feeders with an almost worldwide distribution. Most active stages require blood as a nutritive source and, in the case of adults, for sperm or egg production. Because of the mechanical processes and salivary secretions associated with blood feeding, the tick-host parasitic interaction is complex.

The monoecious ticks may reach up to 2 cm in length and are vectors of important pathogens (viruses, bacteria, rickettsiae, anaplasms, protozoa, and helminths;, since they feed on the blood of their hosts. Unlike vessel feeders (mosquitoes), tick mouth parts bring about more or less deep hollows in the host's skin, which become filled by blood of ruptured blood vessels

Thus, the ticks are pool feeders engorging (in some species for minutes, in others for up to days) large amounts of blood (several times their body weights). During feeding salivary secretions prevent blood coagulation. In some species (e.g., Ixodes spp., Dermacentor spp.) these injected substances are toxic and cause paralysis (tick paralysis), which may lead to death in man and animals. In general, all stages of the tick's life cycle (larvae with six legs, nymphs and adults with eight legs) suck blood. The life cycle of ticks is characterized by periods of starvation which can be of long duration, and by relatively short periods involved with the uptake of enormous concentrated blood meals. The life cycle of an ixodid tick can often have a total duration of 6 years and host attachment may constitute less than 2% of this time.

Starvation periods of more than 3 years are common, and starvation can be particularly extended in some argasid tick species which have been known to survive for up to about 14 years. This ability is very important and has to be considered when dealing with the acute transmission and epidemiology of certain pathogens.

A characteristic of the Acarines is the extreme fusion of body segments, in contrast to the known three body segments head, thorax and abdomen in insects (fig. 13.3, 13.4, 13.5) (and see chapter 12 – anatomy of mites).

Adult tick size spans between 2.2 mm (unfed male) to 13 mm (fed female). In the most common ticks feeding takes place on different animals.

Typical characteristics of ticks:

All stages of the developmental cycle of all kind of ticks parasitic on vertebrates

Stigma behind coxa IV

Ventral toothed hypostom

Peritreme around the stigmen

Haller`s organ on tarsus I

Stages: larvae, nymphs, adults

Ixodidae (hard ticks) and Argasidae (soft ticks).

Fig. 13.3. The anatomy of tick (Ixodes spp.)

The general body of the tick may be divided into capitulum (mouthparts) and idiosoma (body). The idiosoma in turn is comprised of the podosoma (limbs) plus the opisthosoma (torso).

Fig. 13.4. Generalised female ixodid tick

Fig. 13.5. Generalised male ixodid tick

The capitulum of an ixodid tick also called the "rostrum", "the head", or "false head"and the "snout" the capitulum is the moveable anterior extension of the body and includes both the palps and the mouth parts (basis capituli, chelicerae and hypostome) (fig. 13.6).

The capitulum is articulated with the body via a cavity (the emargination in ixodids and the camerstome in argasids), and normally lies in the same plane as the body. It is connected by a soft articulation membrane that allows the capitulum to be flexed (ventrally) or extended (returned to the horizontal axis).

The basis capituli shows two dorsal porose areas in the female. The mouth parts are anterior and well visible from the dorsal aspect.

The chelicerae lie dorsal to the hypostome and support the cheliceral digits which cut into the skin of the host.

The first pair of limbs forms the chelicerae (mandibles) for cutting into the skin of the host, the second pair of limbs forms the palps which position the capitulum for feeding, the third to sixth pairs of limbs are the actual legs used for walking whilst on and off the host.

The four pairs of legs are divided into 6 segments- coxa, trochanter, femur, tibia, metatarsus and tarsus. The coxae are situated on the ventral side of the body and have very limted movement. The other segments are highly flexible but are mainly used by flexing and extending the joints.

The may be folded against the ventral body wall for protection. The segments are connected by a soft articulation cuticle.

The tarsus of each leg bears an apotele (=pre-tarsus), including the claws and and the pulvillus. There is a complex sensory apparatus (=Hallers organ) located on the dorsal surface of the tarsus of leg I. This is very important, as it is the primary organ for determining host location, and detecting host odors and pheromones etc.

Fig. 13.6. The capitulum of an ixodid tick

Fig. 13.7. Diagrammatic representation of an ixodid tick (e.g., Dermacentor sp.) from its ventral side. AN, anus; CH, chelicera; CL, claw; CS, sheath of chelicera; CX, coxa; E, esophagus; EM, pulvillus; FE, festoon; GN, gnathosoma (capitulum); GO, genital opening; H, hypostome; PP, pedipalpus; SA, salivary duct; SC, scutum; STI, stigma; TA, tarsus.

Reproduction / life cycle

In ticks the sexes are separate but sexual dimorphism is less visible in the Argasidae than in the Ixodidae.

In hard ticks, males and females have marked differences in the shape of the scutum, and females possess porose areas (with the exception of Ixodes kopsteini) which are not present in males.

In the genus Ixodes, there is generally further dimorphism in the shape of the gnathosomal appendages. Superficially, soft tick males and females are distinguishable by the shape of the sexual aperture alone. There are principal differences in the reproduction of the two main tick families.

Reproduction in ticks is closely associated with feeding.

In argasid females, feeding and oviposition are cyclical activities which can be repeated several times (up to seven or Moore times)

In ixodid ticks, larvae, nymphs and females all take a single complete meal after which they molt to the next instar, except when the female lays a single batch of eggs and then dies (fig. 13.8).

Thus, feeding and oviposition are each single events in the lifetime of a female.

Fig. 13.8. Life cycle of ticks.

In several species of Ixodes the male is as yet unknown, because mating apparently takes place off the host. The males appear either not to feed, or to feed parasitically on engorged females (fig. 13.9).

The female genital systems of ixodid and argasid ticks are basically similar, consisting of a single ovary with paired oviducts which fuse to become an unpaired common oviduct or uterus. The uterus opens into the vagina which is divided into cervical and vestibular regions

The male reproductive system consists of paired tubular testes which extend from the level of the central nerve mass or genital aperture to about the level of the posterior margin of coxa IV. Apically, the testes extend to become a pair of vasa efferentia which fuse to form a common vas deferens and ejaculatory duct.

Fig. 13.9. Male and female of tick

Musculature

Ticks are typically acarine in having hexapod larvae and octapod nymphs and adults. The legs are jointed and divided into seven segments (coxa, trochanter, femur, genu, tibia, tarsus and pretarsus).

The terminal pretarsus consists of a basal stalk, paired claws and a membraneous pulvillus. The pulvillus is absent in argasid ticks. Each true segment is flexed by an individual flexor muscle, while coxal protractor and retractor muscles provide backward and forward leg movement. Leg extension is brought about by hydrostatic pressure. All legs are ambulatory, but the first pair of legs also aids in sensory orientation.

Alimentary System

The entrance to the alimentary canal, the tubular buccal canal, is formed dorsally by the chelicerae and ventrally by the hypostome. These two parts of the gnathosoma form the anchorage of the tick to the host skin during feeding.

Relative positions of the internal organs of a representative male ixodid tick are presented in figure 13.10. The left hand side has had the midgut removed along the midline as indicated by the jagged edge. The synganglion represents the "brain" of the tick. The tracheal trunks converge to form the spiracle on the tick's ventrolateral surface.

Excretory System

The engorged weight of an ixodid tick can correspond to 50±200 times the unfed weight, while there is less weight increase in feeding argasid ticks. The blood is concentrated 2±3 times during uptake and the volume of the blood in the engorged tick may be only 20% of the total volume of blood imbibed. Some ticks, particularly members of the genus Dermacentor, excrete large amounts of undigested blood through the anus during feeding, i.e., while they are still on the host animal.

In all ticks, the task of removing excess hyposmotic fluid rapidly during or immediately following the blood meal is vital for osmoregulation and is a major excretory effort. In the two main tick families, fluid excretion is achieved by two entirely different mechanisms.

Fig. 13.10. Viscera of a representative male ixodid tick

Nervous System

In ticks there is a very close association between the nervous and the circulatory systems. This is demonstrated by the enclosure of the entire central nervous system within a perineural sinus of the circulatory system; this receives a dorsal aortic vessel and gives rise to vessels enclosing the major nerve trunks. No part of the central nervous system is located within the gnathosoma of the tick, which therefore does not correspond to the head in the generalized arthropod. The brain is located centrally at the level of the second coxa. Ticks can be killed quickly by crushing this region with a hard object (ticks are very resilient: a practical method of destruction is with hot water). The central idiosomal position of the central nervous system makes it poorly accessible for direct investigations. The tick central nervous system is more condensed than in other Chelicerata. It is a synganglion, formed by the fusion of the brain ganglia and the abdominal nerve cord into a single mass.

The nerve trunks arising from the ganglia are formed by axons of both receptor and motor cells. As in other acari, the synganglion is divided into two parts by the esophagus. Cranially, the esophagus lies beneath the synganglion, and then crosses obliquely through the synganglion in a ventrodorsal direction to lie dorsally on the posterior portion before joining the midgut. The cranial, pre-esophageal part of the synganglion consists of the protocerebrum, the optic lobes, the cheliceral and pedipalpal ganglia, and the stomodeal pons or bridge. All ticks examined have been found to possess well-developed photoreceptors, even the „eyeless'' ticks (Aponomma, Ixodes, Haemaphysalis). They also have optic nerves and optic ganglia in the brain. A set of paired nerves extends from the optic lobes, a second set of paired nerves serves the chelicerae, and a third innervates the pedipalps.

The unpaired stomodeal or pharyngeal nerve innervates the pharynx. The postesophageal part of the synganglion gives rise to four pairs of pedal ganglia serving

How ticks survive

Most ticks go through four life stages: egg, six-legged larva, eight-legged nymph, and adult. After hatching from the eggs, ticks must eat blood at every stage to survive. Ticks that require this many hosts can take up to 3 years to complete their full life cycle, and most will die because they don't find a host for their next feeding.

Ecobiology of earthworms

Classification: "Earthworm" is the common name for the largest members of Kingdom Animalia, Phylum Annelida: the "segmented worms" (in Latin, "annellus" means small ring), Class: Clitellata (worms having a clitellum), Subclass: Oligochaeta (meaning "few bristles").

In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female.

Theoretical cladistic studies have placed them instead in the suborder Lumbricina of the order Haplotaxida, but this may again soon change.

Larger terrestrial earthworms are also called megadriles (or big worms), as opposed to the microdriles (or small worms) in the semi-aquatic families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a distinct clitellum (which is more extensive than that of microdriles) and a vascular system with true capillaries.

Earthworms (also called nightcrawlers) are very important animals that aerate the soil with their burrowing action and enrich the soil with their waste products (called castings). From a veterinary viewpoint earthworms are important because they are intermediate hosts, vectors or accumulation hosts.

Parasites with indirect life-cycles spend part of their lives in an intermediate host (earthworm) and then are transferred to the host to which they are best adapted where they become adults and reproduce (fig. 14.1).

A reservoir host can harbour a pathogen indefinitely with no ill effects. A single reservoir host may be reinfected several times. A reservoir host is the primary host of a pathogen.

A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which (usually) some developmental stage is completed.

A paratenic host is similar to an intermediate host, only that it is not needed for the parasite's development cycle to progress. A paratenic hosts serve as "dumps" for non-mature stages of a parasite in which they can accumulate in high numbers.

Amplifying host is a host in which the level of pathogen can become high enough that a vector such as a mosquito that feeds on it will probably become infectious.

From a total of around 6,000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms. These invertebrates (animals without a backbone) range in color from brown to to red, and most have a soft body.

Earthworms range in size from a few inches long to over 22 feet long. The largest earthworms live in South Africa and Australia.

Fig. 14.1. Implications of earthworms in patology

Earthworms are divided into four groups, called ecotypes, based on their behavioral ecology, each of which has a different life style.

Compost earthworms. As their name would suggest, these are most likely to be found in a compost bin. They prefer warm and moist environments with a ready supply of fresh compost material. They can very rapidly consume this material and also reproduce very quickly. Compost earthworms tend to be bright red in colour and stripy.

Compost earthworm species include Eisenia fetida and Eisenia veneta.

Epigeic earthworms live on the surface of the soil in leaf litter. These species tend not to make burrows but live in and feed on the leaf litter, undecomposed plant litter. Epigeic earthworms are also often bright red or reddy-brown, but they are not stripy. These worms are usually small and produce new generations rapidly.

Epigeic earthworm species include Dendrobaena octaedra, Dendrobaena attemsi, Dendrodrilus rubidus, Eiseniella tetraedra, Heliodrilus oculatus, Lumbricus rubellus, Lumbricus castaneus, Lumbricus festivus, Lumbricus friendi, Satchellius mammalis

Endogeic earthworms live in and feed on the soil. They make horizontal burrows through the soil to move around and to feed and they will reuse these burrows to a certain extent. These species ingest large amounts of soil, showing a preference for soil rich in organic matter. Endogeics may have a major impact on the decomposition of dead plant roots, but are not important in the incorporation of surface litter.Endogeic earthworms are often pale colours, grey, pale pink, green or blue. Some can burrow very deeply in the soil.

Endogeic earthworm species include Allolobophora chlorotica, Apporectodea caliginosa, Apporectodea icterica, Apporectodea rosea, Murchieona muldali, Octolasion cyaneum and Octolasion tyrtaeum

Anecic earthworms make permanent vertical burrows in soil. They feed on leaves on the soil surface that they drag into their burrows. They also cast on the surface, and these casts can quite often be seen in grasslands. They also make middens (piles of casts) around the entrance to their burrows. Anecic species are the largest species of earthworms in the UK. They are darkly coloured at the head end (red or brown) and have paler tails.

Anecic earthworm species include Lumbricus terrestris and Apporectodea longa have profound effects on decomposition of organic matter and the formation of soil.

Morphological terms specific for earthworm (fig. 14.2, 14.3)

prostomium peristomium – located above the mouth

body segment – small rings that surround the length of the earthworm’s body; folds in the skin

genital tumescences (GT) – modified epidermis without distinct boundaries, through which follicles of genital setae open

clitellum – swelling in the skin near the head that secretes material to form cocoons.

tubercula pubertatis (TP) – glandular swellings on both sides of the clitellum

setae – bristles (or hairs) that are found on an earthworm’s body; help the earthworm to move

periproct – last segment of the earthworm’s body; contains the anus

anterior – shorter region to one side of the clitellum; head-end of the animal

posterior – longer region is the posterior; tail end of the earthworm

dorsal – small holes located in the furrows down the middle of the earthworm’s back

Fig. 14.2. External morphology of earthworm

Segmented Body

Earthworms are classified in the phylum Annelida or Annelids. Annelida in Latin means, “Little rings.” The body of the earthworm is segmented which looks like many little rings joined or fused together. The earthworm is made of about 100-150 segments.

Fig. 14.3. Internal morphology of earthworms

The segmented body parts provide important structural functions. Segmentation can help the earthworm move.

Each segment or section has muscles and bristles called setae. The bristles or setae help anchor and control the worm when moving through soil. The bristles hold a section of the worm firmly into the ground while the other part of the body protrudes forward.

The earthworm uses segments to either contract or relax independently to cause the body to lengthen in one area or contract in other areas. Segmentation helps the worm to be flexible and strong in its movement. If each segment moved together without being independent, the earthworm would be stationary.

Digestive System

The digestive system is partitioned into many regions, each with a certain function. The digestive system consists of the pharynx, the esophagus, the crop, the intestine and the gizzard (fig. 14.4). Food such as soil enters the earthworm’s mouth where it is swallowed by the pharynx. Then the soil passes through the esophagus, which has calciferous glands, that release calcium carbonate to rid the earthworm’s body of excess calcium. After it passes through the esophagus, the food moves into the crop where it is stored and then eventually moves into the gizzard. The gizzard uses stones that the earthworm eats to grind the food completely. The food moves into the intestines as gland cells in the intestine release fluids to aid in the digestive process. The intestinal wall contains blood vessels where the digested food is absorbed and transported to the rest of the body.

Fig. 14.4. Digestive sistem of earthworm

Circulatory System

Another important organ system is the circulatory system (fig. 14.5). The earthworm has a closed circulatory system. An earthworm circulates blood exclusively through vessels. There are three main vessels that supply the blood to organs within the earthworm. These vessels are the aortic arches, dorsal blood vessels, and ventral blood vessels. The aortic arches function like a human heart. There are five pairs of aortic arches, which have the responsibility of pumping blood into the dorsal and ventral blood vessels. The dorsal blood vessels are responsible for carrying blood to the front of the earthworm’s body. The ventral blood vessels are responsible for carrying blood to the back of the earthworm’s body.

Fig. 14.5. Circulatory system of earthworm

Respiratory System

Earthworms do not have lungs. They breathe through their skin. Oxygen and carbon dioxide pass through the earthworm’s skin by diffusion. For diffusion to occur, the earthworm’s skin must be kept moist. Body fluid and mucous is released to keep its skin moist. Earthworms therefore, need to be in damp or moist soil. This is one reason why they usually surface at night when it is possibly cooler and the “evaporating potential of the air is low.” Earthworms have developed the ability to detect light even though they cannot see. They have tissue located at the earthworm’s head that is sensitive to light. These tissues enable an earthworm to detect light and not surface during the daytime where they could be affected by the sun.

Earthworm Reproduction

Earthworms are hermaphrodites where each earthworm contains both male and female sex organs (fig. 14.6). The male and female sex organs can produce sperm and egg respectively in each earthworm. Although earthworms are hermaphrodites, most need a mate to reproduce. During mating, two worms line up inverted from each other so sperm can be exchanged. The earthworms each have two male openings and two sperm receptacles, which take in the sperm from another mate. The earthworms have a pair of ovaries that produce eggs. The clitellum will form a slime tube around it, which will fill with an albuminous fluid. The earthworm will move forward out of the slime tube. As the earthworm passes through the slime tube, the tube will pass over the female pore picking up eggs. The tube will continue to move down the earthworm and pass over the male pore called the spermatheca which has the stored sperm called the spermatozoa. The eggs will fertilize and the slime tube will close off as the worm moves completely out of the tube. The slime tube will form an “egg cocoon” and be put into the soil. The fertilized eggs will develop and become young worms.

Fig. 14.6. Earthworms reproduction

Ecobiology of gastropods

The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to large. There are many thousands of species of sea snails and sea slugs, as well as freshwater snails and freshwater limpets, as well as land snails and land slugs.

Gastropoda (previously known as univalves and sometimes spelled Gasteropoda) are a major part of the phylum Mollusca and are the most highly diversified class in the phylum, with 60,000 to 80,000 living snail and slug species.

Gastropods are one of the most diverse groups of animals, both in form, habit, and habitat. They are by far the largest group of molluscs, with more than 62,000 described living species, and they comprise about 80% of living molluscs. Estimates of total extant species range from 40,000 to over 100,000, but there may be as many as 150,000 species.

Snail is a common name that is applied most often to land snails, terrestrial pulmonate gastropod molluscs. However, the common name "snail" is also applied to most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into.

When the word "snail" is used in this most general sense, it includes not just land snails but also thousands of species of sea snails and freshwater snails. Snail-like animals that naturally lack a shell, or have only an internal shell, are usually called slugs, and land snails that have only a very small shell (that they cannot retract into) are often called semislugs.

Slug is a common name for an apparently shell-less terrestrial gastropod mollusk. The word "slug" is also often used as part of the common name of any gastropod mollusc that has no shell, has a much reduced shell, or has only a small internal shell.

Lymnaeidae are of major medical and veterinary importance since they act as vectors of parasites (helminths, mainly trematodes) that severely affect human populations and livestock, and cause important economic losses.

Lymnaeids serve as intermediate hosts of at least 71 trematode species distributed among 13 families, including some species of Schistosomatidae and Echinostomatidae, with implications for human health, and Paramphistomum daubneyi, which is of veterinary interest.

Habitat

Some of the more familiar and better-known gastropods are terrestrial gastropods (the land snails and slugs) and some live in freshwater, but more than two thirds of all named species live in a marine environment.

Snails first evolved in marine habitats and later expanded into freshwater and terrestrial habitats. Terrestrial snails live in moist, shady environments such as forests and gardens. Slugs exist on land and in the sea, and there is even one genus of freshwater slugs, Acochlidium.

Gastropods have a worldwide distribution from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized every medium available except the air.

In habitats where there is not enough calcium carbonate to build a really solid shell, such as on some acidic soils on land, there are still various species of slugs, and also some snails with a thin translucent shell, mostly or entirely composed of the protein conchiolin.

Snail Size

Snails grow to a variety of different sizes depending on the species and individual. The largest known land snail is the Giant African Snail (Achatina achatina). The Giant African Snail has been known to grow to lengths of up to 30 cm.

Diet

Terrestrial snails are herbivorous. They feed on plant material (such as leaves, stems, and soft bark), fruits, and algae. Most species of slugs are generalists, feeding on a broad spectrum of organic materials, including leaves from living plants, lichens, mushrooms, and even carrion. Some slugs are predators and eat other slugs and snails, or earthworms.

Anatomy of snails

The anatomy of a snail is very different from many other animals in the world (fig. 15.1).

Snails are distinguished by an anatomical process known as torsion, where the visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. This process is unrelated to the coiling of the shell, which is a separate phenomenon. Torsion is present in all gastropods, but the opisthobranch gastropods are secondarily de-torted to various degrees.

Torsion occurs in two mechanistic stages. The first is muscular and the second is mutagenetic. The effects of torsion are primarily physiological – the organism develops an asymmetrical nature with the majority of growth occurring on the left side. This leads to the loss of right-paired appendages (e.g., ctenidia (comb-like respiratory apparatus), gonads, nephridia, etc.). Furthermore, the anus becomes redirected to the same space as the head. This is speculated to have some evolutionary function, as prior to torsion, when retracting into the shell, first the posterior end would get pulled in, and then the anterior. Now, the front can be retracted more easily, perhaps suggesting a defensive purpose.

However, this "rotation hypothesis" is being challenged by the "asymmetry hypothesis" in which the gastropod mantle cavity originated from one side only of a bilateral set of mantle cavities.

Fig. 15.1. Snail anatomy

Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot, which gives them their name (Greek gaster, stomach, and poda, feet). The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of a gastropod is called a protoconch.

Snails are very different from humans so when we think about body parts, we're often at a loss when relating the familiar parts of a human body to snails. The basic structure of a snail consists of the following body parts:

foot

head

shell

visceral mass

The foot and head are the parts of the snail's body that we can see outside its shell, while the visceral mass is located within the snail's shell and includes the snail's internal organs.

On the head terrestrial snails have primitive eyes (referred to as 'eyespots') that are located on the tips of their upper, longer pair of tentacles. But snails don't see in the same way we do. Their eyes are less complex and provide them with a general sense of light and dark in their surroundings.

The shell

Most shelled gastropods have a one piece shell, typically coiled or spiraled. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum, which in many species acts as a trapdoor to close the shell. This is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined.

Body wall

Some sea slugs are very brightly colored. This serves either as a warning, when they are poisonous or contain stinging cells, or to camouflage them on the brightly colored hydroids, sponges and seaweeds on which many of the species are found.

Lateral outgrowths on the body of nudibranchs are called cerata. These contain a part of digestive gland, which is called the diverticula.

The short tentacles located on a snail's head are very sensitive to touch sensations and are used to help the snail build a picture of its environment based on feeling nearby objects.

Snails have one or two sets of tentacles that are on top of the head. The number of pairs will depend on the species you are describing. Most of the time you will find that the eyes are present on the longer set of them if they have two. You may not always see these tentacles though as all land snails have the ability to retract them.

Snails don't have ears but instead use their bottom set of tentacles to pick up sound vibrations in the air.

The shell of a snail can be very different in size and shape depending on the type of snail it is. Some of them are round while others are flat. Many of them have a spiral design to them. These shells serve as a way to protect them from the environment and even from predators in some cases. The shell of a snail is made up of calcium carbonate. The shell becomes very strong and remains that way as long as the snail consumes a diet that is full of calcium.

Internal Organs

A snail's internal organs include:

a lung

digestive organs (crop, stomach, intestine, anus)

a kidney

a liver

reproductive organs (genital pore, penis, vagina, oviduct, vas deferens)

Circulatory system

Gastropods have open circulatory system and the transport fluid is hemolymph. Hemocyanin is present in the hemolymph as the respiratory pigment.

The heart of the snail is found on the left side and consists of one auricle and one ventricle. The ventricle pumps blue blood through an aortic trunk to all parts of the body through a series of arteries and capillaries. From the capillaries, the blood passes into sinuses, or spaces in the tissues called the hemocoel. From the hemocoel blood passes into the veins and back to the auricle.

Fig. 15.2. Internal anatomy of a snail

Digestive system

The radula of a gastropod is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones, herbivores that use their hard radula to rasp at seaweeds on rocks.

Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over the gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers.

Respiratory system

Almost all marine gastropods breathe with a gill, but many freshwater species, and the majority of terrestrial species, have a pallial lung. Gastropods with a lung belong to one group with common descent, the Pulmonata; however, gastropods with gills are paraphyletic. The respiratory protein in almost all gastropods is hemocyanin, but a pulmonate family Planorbidae have hemoglobin as respiratory protein.

In one large group of sea slugs, the gills are arranged as a rosette of feathery plumes on their backs, which gives rise to their other name, nudibranchs. Some nudibranchs have smooth or warty backs and have no visible gill mechanism, such that respiration may likely take place directly through the skin.

Feeding behavior

Marine gastropods include some that are herbivores, detritus feeders, predatory carnivores, scavengers,parasites, and also a few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the sea floor. In some species that have evolved into endoparasites, such as the eulimid Thyonicola doglieli, many of the standard gastropod features are strongly reduced or absent.

A few sea slugs are herbivores and some are carnivores. Many have distinct dietary preferences and regularly occur in close association with their food species.

Digestive – Snail have sets of jaws inside their mouths used to cut off bits of food. The mouth of a snail is found at the bottom of the head, in close proximity to the tentacles. Just behind the jaws the digestive tract is swollen to form a large buccal mass with muscles attached. This area is covered by the radula, the snail version of the human tongue. The radula moves back and forth very rapidly to grind up pieces of food. It wears away with use, but is continuously replaced since it is formed in a radular sac at the end of the buccal mass and grows constantly, like the human fingernail. The teeth are fastened to the radula in rows. Snails may have up to thousands of individual teeth, with tiny cutting points called cusps. The esophagus leaves the buccal mass and passes from the foot into the visceral mass within the shell to form a crop. Behind the crop is a dilated stomach, which is followed by the long intestine, whose posterior end is dilated to form the rectum. The anus opens into the mantle cavity near the edge of the mantle and the shell.

Endocrine (neuro) – Hormone production is not well documented in mollusks other than gastropods and cephalopods. Antagonistic neurohormonal control of reproductive activity and metabolic processes is performed in the gastropods through cerebral dorsal bodies and lateral lobes or juxtaposed organs. There is a pair of salivary glands line the crop or esophagus, a large digestive gland called the liver empties into the stomach, and a gland secreting albumin.

Excretory system

The primary organs of excretion in gastropods are nephridia, which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in the body cavity, and digestive glands opening into the stomach.

There are two kidneys, or nephridia, in only the primitive gastropods, such as the archaeo- gastropods, while, in the advanced forms, one kidney is small or lost. The kidney plays different roles, depending upon the environment in which the snail lives. Usually, the posterior chamber excretes uric acid and purines, while the anterior chamber has osmoregulatory function. Snails living on the land are uricotelic, this means that to preserve water they excrete almost solid uric acid. Snails living in the water excrete ammonia, and are not uricotelic. The renal aperture (urine opening) is situated in the upper region of the right mantle cavity. The urine produced by the kidneys is expelled here. Terrestrial gastropods reduce water loss by sealing the mantle cavity with an extended mantle collar.

Musculo-skeletal – Most gastropods have a coiled shell in which the visceral mass spirals. Snails move using several important muscles. The columellar muscle is attached to the shell internally and is used to withdraw the snail's body into its shell. The foot, which is mostly muscle tissue, is the main source of propulsion for the snail. The pedal gland at front end of the foot secretes a thin, flat ribbon of mucus for the snail to move along. When the snail is caught in vegetation or out of the water, it may move by "hunching", or muscular contractions of the foot along with a jerky pulling forward of the shell.

Nervous System

A snail's nervous system is made up of numerous nerve centers that each control or interpret sensations for specific parts of the body:

cerebral ganglia (senses)

buccal ganglia (mouthparts)

pedal ganglia (foot)

pleural ganglia (mantle)

intestinal ganglia (organs)

visceral ganglia

Sensory organs and nervous system

The upper pair of tentacles on the head of Helix pomatia has eye spots, but the main sensory organs of the snail are sensory receptors for olfaction, situated in the epithelium of the tentacles.

Sensory organs of gastropods include olfactory organs, eyes, statocysts and mechanoreceptors. Gastropods have no hearing.

In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the 4 tentacles, are the most important sensory organ. The chemosensory organs of opisthobranch marine gastropods are called rhinophores.

The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes, and even to lens eyes. In land snails and slugs, vision is not the most important sense, because they are mainly nocturnal animals.

The nervous system of gastropods includes the peripheral nervous system and the central nervous system. The central nervous system consists of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia.

Nervous and Sensory – The greater portion of the gastropod nervous system, called the brain, consists of nine large ganglia, eight of which are paired. They are connected to each other by commissures and are found around the esophagus just behind the buccal mass.

The snails have more of ability for thinking though than most people give them credit for. Most research shows that they do take part in associative thinking which is based on conditioning and experiences that they take part in.

Large branching nerves originating in these ganglia innervate all parts of the body, while several small ganglia are associated with sense organs. Snails have well-developed eyes at the base of their tentacles. Their sense of hearing is centered in two tiny sacs called statocysts, which contain fluid in which bodies called statoliths are suspended. The snail uses its hearing more as an ability to detect vibrations and maintain a sense of balance. Taste is centered in the mouth region.

Reproductive system

Courtship is a part of mating behavior in some gastropods including some of the Helicidae. Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts.

In many marine gastropods other than the opisthobranchs, there are separate sexes; most land gastropods however are hermaphrodites.

Most terrestrial snails are hermaphroditic which means that each individual possesses both male and female reproductive organs. Although the age at which snails reach sexual maturity varies among species, it may be up to three years before snails are old enough to reproduce. Mature snails begin courtship in early summer and after mating both indivudals lay fertilized eggs in nests dug out of moist soil. It lays several dozen eggs and then covers them with soil where the stay until they are ready to hatch.

While land snails have separate sexes (there are males and females), aquatic snails are hermaphrodites, and they have male as well as female genital organs in a genital apparatus. A snail's fertilization by itself is mostly prevented by the development of sperm and egg cells, which, passing hermaphroditic areas of the genital apparatus are unripe and ripen only when those areas used by male as well as female genital cells are passed. The dart sac serves to transfer a hormone cocktail to the recipient, which is supposed to achieve maximal effectivity of the donator's sperm cells after the copulation. Among the more highly developed snails fertilization takes place internally in the female or at least in the snail acting as female. For that to be possible, fertilization has to be preceded by copulation, during which sperm cells are transferred to the sexual partner. After about two weeks the eggs are laid, although in some species the seminal fluid can be stored for up to year. The eggs look like little white pearls and are laid.

Fig. 15.3. The anatomy of an aquatic snail with a gill, a male prosobranch gastropod.

Light yellow – body;Brown – shell and operculum;Green – digestive system;Light purple – gills;Yellow – osphradium;Red – heart; 1. foot, 2. cerebral ganglion, 3. pneumostome, 4. upper commissura, 5. osphradium, 6. gills, 7. pleural ganglion, 8. atrium of heart, 9. visceral ganglion, 10. Ventricle, 11. Foot, 12. operculum, 13. Brain, 14. Mouth, 15. tentacle (chemosensory, 2 or 4), 16. Eye, 17. penis (everted, normally internal), 18. esophageal nerve ring, 19. pedal ganglion, 20. lower commissura, 21. vas deferens, 22. pallial cavity / mantle cavity / respiratory cavity, 23. parietal ganglion, 24. Anus, 25. hepatopancreas, 26. gonad, 27. rectum, 28. Nephridium.

Snail Strength

Snails can haul up to 10 times their own weight when crawling up a vertical surface. When gliding along horizontally, they can carry up to 50 times their weight.

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