Body small and slender.
Prostomium suboval with a median antenna and with a crescent-shaped anterior part bearing the lateral antennae and the palps. Antennae and palps short, cylindrical, and subequal. No eyes. Caruncle simple, Y-shaped, extending posteriorly on the first segment. Ventral mouth surrounded by large rounded prostomial buccal cushion and first two chaetigers.
Four to twelve pairs of gills, beginning on chaetiger 3 or 4, branched dichotomously several times. Dorsal cirri long on first few and last few chaetigers, others short. Notopodia of first chaetiger each with a strong hook directed forward (P. jeffreysii-parapodium). Rest of notopodial chaetae fine serrated capillary, or harpoon-shaped, or spear-shaped. Ventral chaetae fine capillary and serrated, with or without a basal spur, others forked or spear-shaped (P. jeffreysii-chaetae).
Anus terminal, with median oval papilla.
Up to 15 mm for 24-42 segments.
Inhabits muddy and sandy bottoms of various kinds from shallow subtidal regions to a depth of about 5000 m.
A widespread species in North Atlantic waters, found from northern parts of the North Sea to Skagerrak and Kattegat.