- any annelid of the class Polychaeta, having unsegmented swimming appendages with many setae or bristles.
- belonging or pertaining to the Polychaeta.
- any marine annelid worm of the class Polychaeta, having a distinct head and paired fleshy appendages (parapodia) that bear bristles (chaetae or setae) and are used in swimming: includes the lugworms, ragworms, and sea mice
- of, relating to, or belonging to the class Polychaeta
