Polychaeta (bristleworms; phylum Annelida) Class of annelid worms which possess distinct metameric segmentation. All have bristly parapodia (movable, paired appendages) on each body segment. Eyes may be present. Males and females occur. Most are marine, although some occur in fresh water and on land. The group first appeared in the Cambrian, and impressions of polychaete worms are among the fauna of the Burgess Shale. However, polychaetes are represented in the fossil record largely by burrows (e.g. Skolithus), tubes, and scolecodont assemblages.

Polychaeta (bristleworms; 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.

Polychaeta A class of annelid worms in which each body segment has a pair of flattened fleshy lobes (parapodia) bearing numerous bristles (chaetae). All polychaetes are aquatic and most of them are marine. They include the fanworms (Sabella), which construct tubes of sand, etc., in which they live; and the lugworms (Arenicola) and ragworms (Nereis), which burrow in sand or mud.