n.; n. pl. [L. annulus, ring; Gr. eidos, form]A phylum of segmented or cylindrical ringed worms, encompassing the Polychaeta, mainly free-living and marine, the Oligochaeta, mainly free-living, either terrestrial (earthworms), fresh water, or marine, and the Hirudinoidea or leeches, that are ectoparasitic, fresh water, marine, or rarely terrestrial.
Online Dictionary of Invertebrate Zoology. A.R. Maggenti and S.L. Gardne. 2005.