Describe general characteristics of phylum Annelida. Give one example each class of Annelida.

Characteristics of Annelida:

(i) Body triploblastic, bilaterally symmetrical, soft, elongated, vermiform and cylindrical or dorsoventrally flattened.

(ii) Exoskeleton absent; body is covered by a thin cuticle.

(iii) Alimentary canal is tube-like, complete and extends straight from mouth to anus.

(iv) Reproduction is by sexual means. Sexes may be united (hermaphroditic) or separate.

(v) True coelomate animals with closed blood vascular system. Coelom allows true organs to be packaged in the body structure.

(vi) They live in a variety of habitats. Mostly aquatic, marine or fresh water. Some are terrestrial, burrowing in tubes while some are free-living forms.

Different classes and examples:

Class I: Polychaeta — Nereis (sand worm)

Class II: Oligochaeta — Pheretima (earthworm)

Class III: Hirudinea: Hirudinaria (Indian cattle leech)