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Annelides
- 2. The annelids (Annelida, from Latin anellus, "little ring"), also known as the ringed worms or segmented worms, are a large phylum, with over 17,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
- 3. CHARACTERISTICS - Bilaterally symmetrical and vermiform. - Body has more than two cell layers, tissues and organs. - Body cavity is a true coelom, often divided by internal septa. - Body possesses a through gut with mouth and anus. - Body possesses 3 separate sections, a prosomium, a trunk and a pygidium. - Reproduction normally sexual and gonochoristic or hermaphoditic. - Has no true respiratory organs. - Troch phore lava is present during indirect development.
- 5. Polychaete
- 6. EARTHWORM
- 7. Echiura
- 8. Clitellata
- 9. Classification and diversity Polychaetes - As their name suggests, they have multiple chetae ("hairs") per segment. Polychaetes have parapodia that function as limbs, and nuchal organs that are thought to be chemosensors. Most are marine animals, although a few species live in fresh water and even fewer on land. Clitellates - These have few or no chetae per segment, and no nuchal organs or parapodia. However, they have a unique reproductive organ, the ring-shaped clitellum ("pack saddle") around their bodies, which produces a cocoon that stores and nourishes fertilized eggs until they hatch or, in moniligastrids, yolky eggs that provide nutrition for the embyros. The clitellates are sub-divided into:
- 10. Oligochaetes - ("with few hairs"), which includes earthworms. Oligochaetes have a sticky pad in the roof of the mouth. Most are burrowers that feed on wholly or partly decomposed organic materials. Hirudinea - whose name means "leech-shaped" and whose best known members are leeches. Marine species are mostly blood-sucking parasites, mainly on fish, while most freshwater species are predators.[ They have suckers at both ends of their bodies, and use these to move rather like inchworms]