Phylum annelida


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This is for FYBSc students of University of Mumbai, Maharashtra, India, studying in course one semester I. For further query you may email at

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Phylum annelida

  1. 1. Course I : First semester PHYLUM ANNELIDA (Metamerically segmented and coelomate animals) 1. Annelids are mostly free living and marine, freshwater or soil dwellers. 2. These are soft bodied, triploblastic, bilaterally symmetrical and true coelomates. 3. Body is divisible onto head and trunk with a short tail. It is divided into the segments called as annuli. 4. Excretion is performed by nephridia. 5. Nervous system is well developed, showing brain called as cerebral ganglia.Classification of Phylum -Annelida:I. Class – Polychaeta: (animals with many setae):- 1. Setae are many and are bunched together to give rise to lateral parapodia. 2. Polychaets are marine and either free living or tube dwellers, predatory or filter feeder. 3. Head is distinct with sensory organs like eyes, tentacles, palps etc. 4. Clitellum is absent. 5. Free swimming larval stage is found called as trochophore. 6. A typical example is Nereis 1Prof. S. D. Rathod Copy No VII
  2. 2. Course I : First semesterNereis: - 1. It is marine and free living predatory organism. It is found at the bottom of rocky shore in shallow water hidden in the crevices. 2. Nereis has distinct head with pairs of eyes, tentacles, palps oral cirri and anal cirri. 3. Its mouth is guarded by a pair of claws which helps it to kill prey. 4. It is nocturnal (i.e. active during night). During the night it feeds on small mollusks, crustaceans and worms. Sexes are separate. 5. During breeding period its posterior parapodia are enlarged and thus it becomes heteronereis.II. Class – Oligochaeta: ( animals with few setae):- 1. Setae few and are arranged segmentally. 2. Class includes red worms and earthworms. These are mostly terrestrial or fresh water forms. 3. Distinct head eyes and tentacles are absent, body is cylindrical. 4. Clitellum is usually present. 5. They are hermaphrodite. 6. A typical example is Pheretima (earthworm)Pheretima (earthworm):- 1. Earthworms are burrowers found in surface soil during rainy season. They are nocturnal in habit, during night they come out of their burrows and feed on organic reach soil. 2. Body is made up of 100 to 120 segments and is divided into anterior 13 segments as preclitellar region; middle 14th to 16th segments as clitellar region and posterior remaining part as postclitellar region. 3. Digestive system is complete; mouth is present in first segment guarded by prostomium and anus is present in last segment. 2Prof. S. D. Rathod Copy No VII
  3. 3. Course I : First semester 4. Setae are few and embedded in the skin. 5. Earthworm has integumentary, intestinal and septal nephridia. It is hermaphrodite. Fertilization is cross and internal and development is direct. III. Class – Hirudinea: (Class of leeches):- 1. These are mostly ectoparasitic and fresh water forms. 2. Leeches are sanguivorous i.e. feeding on blood of cattle. To keep blood uncoagulated they secrete an enzyme in its gut called as hirudin; hence the class is named Hirudinea. 3. Head, eyes, tentacles and parapodia are absent. 4. Body made up of definite segment number and is dorsoventrally flattened. Setae are embedded in skin and are arranged segmentally. 5. A typical example is Hirudinaria (common Indian leech) Hirudinaria (common Indian leech):- 1. It is found in fresh water tanks, lakes, ponds, swamps etc. it is ectoparasitic and sanguivorous sucking the blood of fish, frog, and cattle and also human. 2. Body is made up of 33 segments and it grows upto a length of 30 to 35 cm. body is divided into preclitellar region of first eight segments; 9th, 10th and 11th segments includes in clitellar region and remaining 22 segments are called as postclitellar region. 3. A ventral mouth is triradiate and guarded by an oral sucker. Anus is present in 22nd segment on dorsal side. 4. Posterior sucker is made up of fusion of last seven segments. Male genital pore and female genital pores are present in tenth and eleventh segment respectively on ventral side. 3Prof. S. D. Rathod Copy No VII