From ZooTerms (Dictionary of Invertebrate Zoology)
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Annelida also annelids (noun; plural; Latin annulus, ring; Greek 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.