Annelida

Overview

Phylum annelida can be broken into three main groups: Oligochaetes (earthworms), Hirudinians (leeches), and Polychaetes (bristle worms). Primary characteristics of annelids include bilateral symmetry, a complete digestive tract with organ systems, body segmentation, and hydrostatic skeleton. Annelids inhabit a wide range of environments including both terrestrial and marine. They have a variety of feeding modes including being detritivores, deposit feeders, filter feeders, herbivores, predators, and some are even parasitic.

Classes of Annelida present in the Cretaceous of the Western Interior Seaway

Polychaeta