General Topics

Classification of Animals Non Chordates of Class 11

1. Trilobites

They are extinct primitive arthropods which lived during palaeozoic. Almost all the segments of head, thorax and abdomen possessed jointed appendages.

2. Cyclops (Water Flea)

It is fresh-water, microscopic crustacean, with cephalothorax (head + first thoracic segment), thorax and abdomen. Head bears antennae, antennules, a single median eye, mandibles,maxillae and maxillulae. Thorax bears appendages but the same are absent from abdomen. There is no heart. Movement of gut helps in blood circulation. Respiration is rectal by passing water current through anus. Cyclops is intermediate host of Guinea worm and Broad tapeworm.

3. Crabs

The crab is carnivorous. It captures the prey by chelipedes. They are found in both fresh-water & tidal regions of sea. e.g., Paratelphusa (fresh-water), Scylla serrata (marine edible crab) & Cancer (rock crab).  The crab has a broad, flat, disc-like cephalothorax. The compound eyes are stalked. Both pairs of antennae are very short. The first pair of thoracic legs are very large, chelate and called chelipedes.

The abdomen is small, triangular and segmented.

4. Hermit Crab

He crab lives inside empty molluscan shells.

5. Prawn (Palaemon)

Palaemon is nocturnal, omnivorous, fresh-water but bottom feeder. It is edible. The body is divisible into cephalothorax and abdomen. Respiration occurs through gills. Eyes are situated at the tips of movable stalks. A toothed rostrum and two pairs of lateral spines occur nearby. Thorax contains 3 anterior pairs of maxillipedes for feeding and 5 pairs of legs. Abdomen bears 6 pairs ofappendages, 5 pairs of swimmeretes and one pair of uropods. Abdomen ends in a pointed telson.

6. Centipede (Scolopendra) 

The centripedes or “hundred leggers” are cosmopolitan in occurrence. The body is elongate and dorsoventrally flattened with a small head and 21-segmented trunk. The head bears two long many-jointed antennae, two groups of ocelli and mouth. Each of the trunk segments bears a pair of legs, except the one posterior to head that bears a pair of poison claws of maxillipedes.

Centipedes are carnivorous in diet.

7. Millipede (Julus)

The millipedes are called ‘thousand leggers’. The body is elongated and somewhat cylindrical with a small head and a large 40 or more segmented trunk. The trunk segments are diplosegments, each with two pairs of jointed legs attached ventrally to the segments. The anterior four segments constitute the thorax. Its first segment is legless; the second, third and fourth segments are with only single pair of legs. On most of the trunk segments are located stink glands or odoriferous glands. Their secretions are toxic to other animals.

8. Scorpion

Scorpion is nocturnal, terrestrial and carnivorous. Its body is divisible into prosoma, mesosoma and metasoma. Prosoma is unsegmented. It has a pair of small chelicerae, a pair of large pedipalps, three groups of simple eyes and four pairs of walking legs. Mesosoma is broad and has seven segments. Metasoma has 5 segments. The last segment has an anus and a curved pointed telson or sting. The sting has a basal swollen ampulla (with two poison glands) and a spine. The sting is meant for paralysing or killing the prey. Male scorpion is smaller than the female. Courtship dance occurs. After mating, the male scorption may be killed by female. Scorpions are viviparous. Respiration occurs through book lungs.

9. Spider (Aranea)

Webs are woven by 3-4 pairs of tubercles having spinnerets and underlying silk glands. They occur on the under-surface of abdomen. Web is used for trapping insects and other small animals. They are paralysed by poison from chelicerae. Only fluid is sucked. Eyes are simple. Chelicerae and pedipalpi occur. Walking legs are four pairs. Respiratory organs are tracheae and book lungs.

Male spiders are commonly smaller.

10. Insecta : General account.

(a) Metamorphosis : Metamorphosis is the phenomenon of passing through different juvenile forms before becoming adult or imago. It is controlled by juvenile hormone secreted by corpora allata. There are five types of development.

(i) No Metamorphosis or Ametabolic Development : The newly hatched young ones are similar to adult in all aspects except size, sex organs or armature, e.g., Silver Fish (Lepisma).

(ii) Incomplete Metamorphosis or Hemimetabolic Development : The young ones (nymphs) differ from adults in mode of living, size and some structural details, e.g., Dragonfly.

(iii) Gradual Metamorphosis or Paurometabolic Development : The young ones or nymphs resemble imago but do not have wings, armature, external genitalia and some other structures. The adult structure is attained after a few moultings, e.g., Grasshopper, Cockroach, Praying Mantis, Bed-bug, etc.

(iv) Complete Metamorphosis or Holometabolic Development : The young one or larva is completely different from imago in external structure, many internal organs and mode of living. The young one is  worm-like and called larva. A full grown larva suspends feeding and movments. The inactive stage is termed pupa. The insects with such a metamorphosis have four stages in the life history: egg, larva, pupa and adult. Larva is named variously in different groups - wriggler (aquatic larva of mosquitoes),  grub (beetle), caterpillar (butterfly, moth), maggot (housefly), etc.

(v) Hypermetamorphosis or Hypermetabolic Development : It is a type of development where each larval stage or instar differs from the other in habits, food and mode of living, e.g., Blister Beetle.

(b) Compound Eyes : It is an eye having a number of image forming units called ommatidia. Compound eye gives mosaic vision.

(i) Structure : Compound eyes consist of a large number of individual elements called the ommatidia.  The outermost layer of the eye forming the cornea is the transparent cuticle. In a surface view the cornea, exhibits a large number of squares or facets, giving the appearance of a graph paper. Below each facet lies one ommatidium. The ommatidia are alike in structure. Each corneal facet thickens in the centre to form a biconvex corneal lens. Beneath the lens lie two corneagen cells which are modified epidermal cells and secrete a new cornea as soon as the old one is cast off in moulting. Beneath the corneagen cells lie four elongated cone cells or vitrellae which constitute a transparent, homogeneous crystalline cone. The part of the eye from cornea up to the extreme ends of cone cells is known as the dioptrical region, which focusses the light upon the inner sensitive part or receptor region of the eye. The inner ends of cone cells lie upon the rhabdome, which has a transversely striated appearance. The rhabdome is secreted and surrounded by seven elongated retinal cells. The rhabdome and the retinal cells together form the receptor region of the eye. Each ommatidium is cut off from its neighbours by a sheath of movable, amoeboid, dark pigment cells or chromatophores.

(ii) Mosaic vision : Each ommatidium is capable of producing a separate image of a small part of the object seen. Apposition image. Each ommatidium responds to a fragment of the total field and then these fragmented images are fitted together into a single general picture. It is known as an apposition image, the sharpness of which depends upon the number of ommatidia involved and the degree of their isolation from one another. In butterflies, which are night-blind, the eyes are permanently set in this condition and are suited to see only in bright light. It functions best at short distances only.

Superposition image. An overlapping of the adjacent points of image occurs so that a continuous image, called the superposition image, is obtained. It is not sharp but the animal gets some sort of idea of the objects moving about in the surrounding. In some insects, like moths and fireflies, the eyes are permanently set like this, so that they are well adapted to see at night but are day-blind.

(c) Ecdysis : Ecdysis or moulting is the process of casting off the dead rigid outer covering of the animal body during its growth. Moulting is controlled by a steroid hormone ecdyson (ecdysone) produced by prothoracic glands. The state of larva between two moultings is called instar. The period between two moultings is stadium.

(d) Mouth Parts : Insect mouth parts comprises a pair of mandibles, two pairs of maxillae, a labrum or upper lip, a lingua or hypopharynx and epipharynx. They are modified variously to perform different functions.

(i) Biting and Chewing : The mandibles are toothed and are used for crushing food. Maxillae help in holding food, e.g., cockroach, silver fish, termites, grasshopper.

(ii) Piercing and Sucking : Mosquitoes and bugs have this type of mouth parts. Mandibles, first pair of maxillae and hypopharynx are needle-like and take part in piercing. Second pair of maxillae form sucking tube.

(iii) Siphoning : It occurs in butterflies and moths. Maxillae, labium and second pair of maxillae are reduced. Parts of first pair of maxillae form a sucking tube which normally remains coiled below head.

(iv) Chewing and Lapping : The mouth parts are found in honeybee. Mandibles are used in collection, breaking and construction. A sucking tube is present. Certain parts are used for opening the path of nectar glands.

(v) Sponging (Sucking and Lapping) : In houseflies, mandibles are absent. First pair of maxillae are reduced. Second pair of maxillae form a grooved labium. Labellum has pseudotrachea (channels) for picking up liquified (with saliva) food which is then passed into food canal formed by labrum and hypopharynx lying in the groove of labium.

(e) Silver Fish (Lepisma saccharina) : It is small wing-less, soft-bodied insect. The mouth parts are of biting type. The compound eyes are reduced or vestigeal. Abdomen is eleven segmented. They cause considerable damage to ooks and clothes.

(f) Stick Insect (Carausius morasus) : The insect shows mimicry because its long thin body resembles a twig. It is also called walking stick. Wings are reduced.

(g) Grasshopper (Ak Grasshopper, Poecilocerus pictus) : It is short-horned, diurnal insect common on Calotropis plants. There are two pairs of wings. Male Grasshopper produces sound by rubbing edges of wings, or metaleg with fore-wing of its side.

(h) Locust (Schistocerca gregaria) : There are many locusts but Schistocerca gregaria (desert locust) and Locusta migratria (migratory locust) are common ones. They are the most destructive of all insects. When conditions are favourable, it reproduces enormosuly and passes into gregarious phase. Then the swarm migrates to other places. They feed on leafy vegetation. They have biting and chewing mouth parts,

and powerful hind legs are adapted for jumping. Locusts are serious plant pests.

(i) Laccifer or Tachardia lacca (Lac infect) : Lac is secreted by female insect for protection during unfavourable conditions. Lac Research Institute is situated in Ranchi, Bihar.

(j) Dragon Fly : The wings are kept horizontal at rest. Legs are not used for walking. They are prehensile. Copulation occurs in flight. Respiration in nymphs is through rectal chamber.

(k) Rat Flea (Xenopsylla cheopis) : The wingless insect has long legs for jumping and strong claws for clinging. Mouth parts are of piercing and sucking type. The insect is an ectoparasite of rats and humans feeding on their blood. It may transmit Pasterella pestis or germs of bubonic plague from rats to humans.

(l) Butterfly & Moth

General Topics

(m) Silk Moth : The most common silkworm is Bombyx mori. It is found on mulberry leaves in India. The silkworm is dioecious. The female lays about 300-500 eggs in clusters upon the mulberry leaves. The larva which hatches from the egg is called the caterpillar. It possesses mandibulate mouth-parts with which it feeds upon the mulberry leaves. When fully grown, the mature caterpillar larva or silkworm stops feeding. It develops a pair of salivary glands which secrete liquid silk. The liquid silk flows into two ducts to a common exit tube, the spinneret. The silk threads wrap around the body of the caterpillar to form the pupal case or cocoon. Within a fortnight the caterpillar develops inside the cocoon, and becomes the pupa or chrysalis. Pupa forms the adult moth which secretes an alkaline fluid to moisten one end of the cocoon in order to escape to outside.

Sericulture : The rearing of silk moths in order to obtain silk for commercial purpose is called sericulture. For obtaining the commercial silk, the cocoons are treated with hot water to kill the pupae inside. The silk is unwound from the cocoons and twisted into threads of commercial silk. Silk producing species are Antheraea paphia producing tassar silk, A. assama producing munga silk. But best silk is produced by B. mori. Central Sericulture Station is situated in Barhampur, West Bengal. Silk Research and Training Institutes are situated in Ranchi (Bihar), Mysore (Karnataka), and Dehradun (Uttar Pradesh).

(n) Termites : The termites are social insects, living in colonies with well-organized castes. There are two main castes of termites: fertile males and females and sterile males and females. These are differentiated into workers, soldiers, winged (alate) and non-winged (dealate) reproductive individuals and nasutes. The workers are wingless forms. They collect food, look after the young, attend to the reproductive forms and construct nests and passage ways, etc. The soldiers possess large and strong mandibles. They protect the colony. In some termites the soldiers are replaced by nasutes, which are also wingless and possess a rostrum that pours a sticky secretion for destroying enemies and dissolving hard substances. Reproductive male and female termites are called king and queen respectively. They are wingless but develop from sexual winged forms live in royal chambers. Most termites build underground nests. Number of termites build high and large mounds raised high up the ground. Certain termites build their nests inside the wood or on the branches of trees. Cellulose is the principal foodstuff  of termites. The cellulose is supposed to be digested either by bacterial or protozoan decomposition or by the enzyme, cellulase.

(o) Honey Bee : A hive consists of a vertical sheet of wax with a number of hexagonal cells for rearing young bees (brood cells), storing food (storage cells), royal chamber and chamber for themselves. Bee is a social, polymorphic and colonial insect. It has three main castes-queen, drones and workers. Queen is the only fertile female of the colony which continues to lay eggs for 2-5 years. Drones are male honey bees.

They develop from unfertilized eggs. Drones and virgin queens take part in nuptial flight. After copulation the drones are not allowed to come back into hive. Workers are sterile females. Scout bees search for food and intimate the same to worker bees by dances - round dance for less than 75m and tail wragging dance for longer distances. Prof. Karl Von Frisch got Nobel Prize for decoding the language of bee dances. Workers have a pollen collecting apparatus, honey storing mechanism and wax secreting glands. Young workers secrete royal jelly. Royal jelly is given to queen or potential queens. Honey contains simple sugars (fructose & levulose), vitamins and minerals. It is a tonic, laxative and sweetening agent. True product of honey bee is bees wax.

(p) Housefly (Musca nebulo, M. domestica) : It is active in warm months and inactive during winter when it may die. The body is differentiated into head, thorax and abdomen. Head has two compound eyes, three simple eyes, a pair of antennae and sponging type of mouth parts. Labrum forms proboscis, mandibles are absent, maxilla is in the form of maxillary palps, labrum & hypopharynx are represented by chitinous sclerites. Only liquid food can be taken by housefly. Solid food is first liquified by action of saliva, then taken by capillary action into pseudotrachea. Mesothorax bears a pair of transparent wings.

Metathorax has a pair of halters for balancing. Female fly lays eggs in moist organic debris like dung. Larva is called maggot. Housefly transmits a number of diseases like conjunctivitis, trachoma, gangrene, plague, cholera, dysentry, poliomyelitis, diarrhoea, typhoid, etc.

(q) Mosquito : Mosquito are small nocturnal insects having a pair of wings and mouth parts modified for piercing and sucking. Mandibles are absent in males. Pedicel of antenna has a proprioreceptor called Johnston’s organ for perceiving vibrations. Male mosquitoes usually feed on flower sap or nectar while female mosquitoes feed on blood. The common mosquitoes are Anopheles, Culex and Aedes.

(r) Glow Worm : Wingless female and larva of certain beetles like Lymphyris noctiluca which emits greenish light. Also yields luciferin.

(s) Cochineal Insect : (Cactus Scale - Insect, Dictylopius coccus) yields red dye.

(t) Spanish Fly (Lytta vesicatoria) : yields canthridine from dead bodies.

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