The annelids (Phylum Annelida) are also called the segmented worms due to their segmented bodies. This group includes the most familiar of all invertebrate worms. Earthworms, freshwater worms, leeches, and marine worms are all annelids.

This group is also called "bristle worms" because most annelids have tiny chitinous bristles called setae. The setae help terrestrial annelids grip their surroundings, and they aid aquatic forms with swimming.

Annelids are worldwide in distribution, and they are found in marine environments, fresh water, and terrestrial soil. Some annelids are predators, others are vegetarians, and some leeches are bloodsuckers.