Oligochaeta () is a class of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, and including all of the various earthworms. Specifically, the oligochaetes () contain the terrestrial megadrile earthworms (some of which are semiaquatic or fully aquatic), and freshwater or semiterrestrial microdrile forms, including the tubificids, pot worms and ice worms (Enchytraeidae), blackworms (Lumbriculidae) and several interstitial marine worms.