CLASSIFICATION OF ANNELIDA
Phylum Annelida is further classified into 4 different classes;
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POLYCHAETA
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Chiefly marine, some are fresh water.
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Body segmentation is both external and internal.
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Setae numerous, on lateral parapodia.
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Clitellum absent.
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Dioecious animals.
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Trochophore larval stage is seen.
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Ex- Neris.
2. OLIGOCHAETA
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Mostly terrestrial, some are fresh water.
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Segmentation is both external and internal.
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Parapodia is absent. Setae few embedded inside the skin.
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Clitellum is present for cocoon formation.
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Monoecious animals.
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Development is direct i.e., no larval stages seen.
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Ex- Pheretima.
3. HIRUDINEA
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They may be marine, fresh water or terrestrial in habitat. Generally ectoparasites.
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Segmentation external, without any internal septa.
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Parapodia and setae are absent.
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Monoecious animals.
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Development is direct. No larval form is found.
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Ex- Leech.
4. ARCHIANNELIDA
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Marine animals.
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Body segmentation is chiefly internal.
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No parapodia and setae are found.
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Dioecious animals.
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Development is indirect i.e., through Trochophore larval stage.
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Ex- Polygordius
