; phylum Annelida)
A class of worms which possess distinct metameric segmentation. They have numerous chaetae borne in sheaths on the parapodia on each body segment. Eyes and tentacles may be present. Most polychaetes are dioecious but a few species are hermaphrodites. Most are marine, although some occur in fresh water and on land. The group first appeared in the Cambrian (polychaetes are the only annelids to have a fossil record) and it contains more than 5000 species.
Subjects: Earth Sciences and Geography — Zoology and Animal Sciences.