Annelida

Definition

Annelida is a phylum of segmented worms characterized by their ring-like body segments called annuli. They include earthworms, leeches, and marine polychaetes.

5 Must Know Facts For Your Next Test

1. Annelids have a true coelom that functions as a hydrostatic skeleton.
2. They possess both longitudinal and circular muscles for movement.
3. Annelids exhibit metamerism, meaning their bodies are divided into repeating segments.
4. They have a closed circulatory system with blood vessels.
5. Most annelids have specialized structures called setae or chaetae for locomotion.

Review Questions

• What type of body cavity do annelids possess?
• How do annelids achieve movement?
• What is the significance of metamerism in annelids?

Related terms

Mollusca: A diverse phylum of soft-bodied animals often protected by a hard shell, including snails, clams, and octopuses.

Setae: Bristle-like structures found on annelids that aid in locomotion.

Polychaetes: A class of marine annelid worms known for their parapodia and numerous bristles.