Annelida is a phylum of segmented invertebrate worms, including earthworms, leeches, and tube worms. Their bodies consist of repeating segments called somites, each containing coelomic cavities that support internal organs. Annelids have a well-developed circulatory system.
Earthworms decompose organic matter and enrich soil. Leeches feed on blood in aquatic habitats. Tube worms live in protective calcium carbonate tubes in reefs, vents, and the deep ocean.