11th Class Biology Animal Kingdom Some representative animals

(1) The common Indian earthworm, Pheretima posthuma belong to the class oligochaeta of the phylum Annelida. It is found in every part of the world. It lives in damp soil and burrow in lawns, fields, garden etc. rich in humus. Earthworm is nocturnal i.e., active during night.

(2) The generic name Pheretima was first used by Kinberg in 1867. Our knowleage of Pheretima is mainly due to the work of Karm Narayan Bahl (1926).

(3) Body is cylindrical, bilaterally symmetrical, elongated with metameric segmentation. Earthworm shows both external and internal segmentation. The number of segments is about 100-120, the length is about 150 mm.

(4) Earthworm is brown or clay-coloured. This is because of the pigment porphyrin. Numerous granules of porphyrin pigment are found scattered in the circular muscle layer of body wall. Porphyrin protects the body from the injurious effects of bright light.

(5) The first segment is peristomium or buccal segment which bears mouth. Anus is located on the last segment.

(6) Three regions in body of earthworm are ? Preclitellar region (1 - 13), Clitellar region (14, 15, 16)  and Postclitellar region (17 - last).

(7) Nephridiopores of integumentary nephridia 200-250 per segment found in all segments except the first six. Clitellar segment contains 2000 nephridiopores per segment, so called-forest of nephridia?.

(8) In the body wall 11 pores concerned with reproduction. They are - Spermathecal pores in the intersegmental grooves of 5/6, 6/7, 7/8 and 8/9 (4 pairs). Female genital pore midventral on segment 14th. Male genital pores ventrolaterally (1 pair) on segment 18th.

(9) Male genital papillae are present on segments 17 and 19 (2 pairs).

(10) Body wall is dermomuscular, consists of cuticle, epidermis, muscular layers and coelomic epithelium. Epidermis consists of tall, columnar cells of four types ? Supporting cells (major part), Glandular cells (Goblet and albumin), Basal cells and Sensory cells.

(11) All segments except the first, last and clitellar segment contain setae (perichaetine arrangement). Setae are 'S-shaped, yellowish and chitinous, 80-120 segment. Setae and contraction of muscles help in locomotion.

(12) The body cavity of earthworm is true coelom (schizocoel) as it is formed by the division of mesoderm. The coelom is filled with milky white alkaline coelomic fluid. Coelomic fluid contains different types of carpuscles. These are granulocytes (phagocytes), most numerous mucocytes, circular nucleated cells (leucocytes) and chloragogen cells (yellow cells).

(13) Chloragogen cells are small, star-shaped, yellow cells concerned with storage of reserve food, deamination of proteins, formation of urea and also excretory (analogous to the liver of vertebrates).

(14) The alimentary canal of earthworm is a straight tube, representing a ?tube within tube plan, Location of different part of alimentary canal are -

Buccal chamber         :                               \[1-2\frac{1}{2}\]

Pharynx                         :                               \[2\frac{1}{2}-4\]             

Oesophagus                :                              5-7        

Gizzard                           :                              8

Stomach                         :                              9-14

Intestine                        :                               15 onwards

Roof of pharynx contains pharyngeal glands containing chromophil cells secreting mucus and proteases. Gizzard is a thick muscular organ, cavity lined by tough cuticle for grinding. Wall of stomach contains -calciferous glands- the secretion of which neutralizes the acidity of soil.

(15) Due to presence of typhlosole the intestine is divided into three region - Pretyphlosolar region, typhlosolar region, post typhlosolar region. Intestinal caeca arise from segment  26 and extend forward upto segments 22 or 23.

(16) Typhlosole is a highly glandular, vascular longitudinal ridge increasing the area for absorption of digested food.

(17) Earthworms are omnivorous, undigested particles as faeces are called as 'casting'.

(18) Blood vascular system of earthworm is closed type. Blood is red in colour, respiratory pigment haemoglobin is dissolved in the blood plasma .

(19) The main longitudinal blood vessels are three -

(i) The dorsal blood vessel

(ii) The ventral blood vessel

(iii) The subneural blood vessel

(20) Important transverse vessels in first 13 segments are -

Lateral hearts (segments 7 and 9), Anterior loops (segments 10 and 11) and, Lateral oesophageal hearts (segments 12 and 13).

(21) Dorsal blood vessel is distributive in segments 1 to 13. Flow of blood in dorsal vessel is from posterior to anterior direction.

(22) Ventral vessel is found below alimentary canal, single, blood flows anterior to posterior direction.

(23) Blood glands are three in number and present on 4th, 5th and 6th segments. These produce blood cells and haemoglobin.

(24) Lymph glands are present on both sides of dorsal blood vessel from segment 26th and those behind it (one pair per segment, small and whitish). Lymph glands are supposed to produce certain phagocytic cells.

(25) Earthworm respires, but has no respiratory organs, exchange of gases takes place through moist skin. The absorptive area of earthworm is more than its volume, so earthworm does not require any respiratory organ. If the skin of the earthworm dries, it cannot respire. it dies due to asphyxia.

(26) Excretory organs of earthworm are segmental nephridia ectodermal in origin, analogous to vertebrate kidney.

(i) Pharyngeal nephridia are situated in the segments 4, 5 and 6. They open in the anterior part of alimentary canal, i.e. buccal cavity and pharynx. They are without nephrostome and are enteronephric type.

(ii) Integumentary nephridia are scattered in the body wall. They are smallest, V-shaped without nephrostome and are exonephric type.

(iii) Septal nephridia are the largest, attached to both facees of each intersegment septum behind 15th segment.

(27) Septal nephridia are the only nephridia with nephrostome or funnel. The terminal duct opens into septal excretory canal. Septal nephridia are enteronephric finally excretory products are poured into intestine. Earthworms are mainly ureotelic.

(28) Earthworm has a well developed nervous system; it has a brain but no head. Brain lies above pharynx, made up of a pair of suprapharyngeal (cerebral) ganglia.

(29) Earthworm has no eyes, photoreceptors are used to judge intensity and duration of light, do not have the capacity of vision.

(30) Earthworm are hermaphrodite (monoecious) but fertilization is cross type due to protandrous condition.

(31) In earthworm reproductive system consist of the following organs -

(32) Spermatheca are used to store after copulation (open outside on intersegmental groove 5/6, 6/7, 7/8, 8/9).

(33) Copulation occurs between two earthworms generally at night during rainy season. Fertilization is external and occurs in cocoon. Cocoons are formed by glandular clitellum. A cocoon may contain many fertilized eggs, but only one embryo develops, other eggs serve as nurse cells.

(34) Cleavage is holoblastic and unequal, development is direct without any larval stage.

(35) One of the oldest use of earthworm; it is used as bait for catching fish. Earthworms are friends of farmers because they enrich the soil by nephridial excretion, it increases the fertility of soil.

It is commonly known as Indian cattle leech. It is sanguivorous (feed on blood) segmented animal that live in ponds, streams, rice fields etc. It is ectoparasite on cattle and human. The body is soft, flattened and slimy. The dorsal side is yellowish green while the ventral side is orange. Botryoidal tissue present in coelomic space.

The body is divisible into 33 segments. Each segment further appear subdivided superficially by annuli. Each segment from 6-22 bear a pair of ventral nephridiopore. During breeding season a temporary clitellum develps on 9, 10 and 11 segments. The leech bears two suckers. The anterior sucker encloses the mouth. It acts as a feeding locomotory and prehensile organ. The posterior end bears a large disc-shaped sucker that helps in locomotion and anchorage. It comprises the last seven uniannulate segments. Anus lies ahead of posterior sucker. Triradiate mouth is present at its bottom. The saliva of the leech contains an anti-coagulant, called hirudin which prevents clotting of blood during blood meal. There are present five pair of eyes on the dorsal surface. It is hermaphrodite but cross-fertilisation occurs. Development is direct. Prof. M.L. Bhatia has given a detailed morphology of H. granulosa.

It is commonly called clam worm or sand worm or rag worm whish is found on the sea shore in the tubular burrow. Nereis is unisexual and its reproductive phase is called Heteronereis. Heteroneresis have two reasions - epitoke or posterior sexual region and atoke or anterior region without masses of developing gametes. The phenomenan of transformation of nereis into heteronereis is called epitocky. The gametes are liberated through mixonephridia. Fertilization occurs in sea water. During development trochophore larva is present. The prominent head consists of prostomium and peristomium. The prostomium bears a pair of small tactile tentacles and a pair of stout palp. On the dorsal surface of the peristomium there are present two pair of black eyes. Peristomium has four pairs of long tentacles (cirri). Pharynx is everted for ingestion of food.  Each segment bears laterally one pair of fleshy projection, the parapodia, used in swimming. The last segment has an anus. The anal segment is devoid of parapodia but bears a pair of elongated anal cirri.

It is a marine worm which lives in the crevices of the rocks. It has only traces of segmentation but sexual dimorphism is extremely exhibited. The female has an ovoid and unsegmented body covered with papillae. It is provided with a prostomial bifurcated proboscis homologous to annelids. There is only one pair of large ventral chitinous setae. The male is small and is reduced to a minute size of Turbellaria and lives in the body of the female. The larva of Bonellia has the potentialities of both male and feamle. If they develop independently they become females, but if they come in contact with female, they develop into males.

The Aphrodite is a marine polychaete which is commonly called the 'sea mouse'. It is found burried in the mud or sand or crawling on the sea bed. The body is oval, broad and dorso-ventrally flat and consists of 30-35 metameres. The body is covered with scales or elytra which are modifications of dorsal cirri of parapodia and are respiratory in function. The head is small and consists of a peristomium and a prostomium. The prostomium bears a pair of eyes, a short tentacle and a pair of long palps. During movement the animal changes colour from golden to peacock blue. The animal is commonly found in Atlantic and Mediterranean seas.

Common Names