Phylum Annelida

Phylum Annelida (Latin annulus = ring) includes animals such as Nereis, Pheretima (earthworm) and Hirudinaria (leech), and its members are commonly called ring worms or segmented worms. They may be aquatic, ectoparasitic, free-living, or burrowing in moist soil.

Annelids show bilateral symmetry with true metameric segmentation — the body is divided into a linear series of similar segments. A specialised, glandular region of the body called the clitellum is present in some members (visible as a prominent band in earthworms).

Locomotion is powered by longitudinal and circular muscles, aided by locomotory structures that vary by group: bristle-like setae in earthworms, paired lateral outgrowths called parapodia in Nereis, or suckers in leeches. …