NEET Biology Notes Animal Kingdom Earth worm
Earth worm
Earth worm
Earthworm (Pheretima posthuma) is brown or clay-coloured because of the pigment porphyrin. Three region in the body of earthworm are preclitellar region (1-13), clitellar region (14, 15, 16) and postclitellar region (17-last). Pores in the body wall concerned with reproduction are 11. They are spermathecal pores present in the intersegmental grooves of 5/6, 6/7 7/8 and 8/9 (4 pairs). Female genital pore is midventral on 14th segment.
Male genital pores are ventrolateral (1 pair) on segment 18th. Male genital papillae are present on segment 17 and 19 (2 pairs!. Setae helps in locomotion. Body cavity is a true coelom (schizocoel), containing milky white alkaline coelomic fluid. Chloragogen cells are small yellow cells, concerned with storage of reserve food, formation of urea and also excretory (analogous to the liver) in function.
Typhlosole is a highly glandular, vascular longitudinal ridge increasing the area for absorption of digested food. Blood vascular system of earthworm is closed type. Blood is red in colour, respiratory pigment haemoglobin, dissolved in the blood plasma. Earthworm respires, but has nr piratory organs, exchange of gases takes place through moist skin.
Excretory organs are segmental nephridia analogous to vertebrate kidney. Spermatheca are used to store sperms after copulation. Cocoons are formed by glandular clitellum. Cleavage is holoblastic and unequal, development is direct without any larval stage.
Hirudinaria
Hirudinaria is a freshwater and ectoparasitic annelid. It is sanguivorous and feeds upon the blood of cattle. Blood is stored in a 10-chambered crop and blood clotting is prevented by mixing an anticoagulant called hirudin. It shows cutaneous respiration. It is hermaphrodite but show cross-fertilisation due to protandrous condition. Development is direct.
Body is elongated and divided into 33 metameres by annuli. Male and female gonopore lie on ventral side of 10th and 11th segment respectively.
Phylum-Arthropoda
This phylum is the largest in the animal kingdom comprising of more than 75% of the animal species.
These are free-living, aquatic (freshwater or marine) or terrestrial and some are in parasitic forms also. Body is elongated and segmented, usually distinguished into regions-like head, thorax and abdomen. Body has exoskeleton made up of a hard, impermeable substance called chitin. Digestive system is complete.
Circulatory system is of open type. Blood flows freely in the body cavity (haemocoel). Respiration through gills or trachea or book lungs. Excretion through coxal glands or Malpighian tubules. Nervous system consists of a nerve ring and double ventral nerve cord.
Locomotory organs are represented by segmentally arranged jointed appendages. Cilia are totally absent. Reproduce sexually, sexes are separate. Development may be direct or indirect. Luminescent insects Photinus, Lampyres and some other genera bear light producing organs on abdomen, e.g. mosquito, cockroach, Apis (honeybee), Aranea (spider), Palaemon (prawn), Scolopendra (centipede).
