Body conical, gradually tapering to the posterior end.
Many chaetigers; a narrow achaetigerous part present between the thorax and abdomen. Thorax with 6 chaetigers, all with notopodial capillary chaetae and neuropodial uncini. First chaetiger without collar chaetae.
Crown with 9-15 pairs of long radioli, without a basal membrane.
Operculum and peduncle without spines or pinnules, with a brownish concave distal plate bearing a knob-like projection within the funnel-shaped ampulla.
Anterior border of thorax with numerous red lensed eyes. Thoracic membrane extends to the last thoracic segment (P. tridentatus-chaetae). Thoracic notopodial chaetae are capillaries with broad wings; uncini quadrangular, with numerous small teeth. Abdominal neuropodial chaetae chisel-formed, with one long, sharp projection and numerous small teeth on the upper border. Abdominal capillary chaetae long; uncini like those of the thorax.
Up to 30 mm long.
Translucent; triangular in cross-section, with a median keel which extends over the aperture as a 'tooth', and flanges against the substratum which end as two additional teeth if the anterior becomes erect.
Crown dark red, with 2 brown cross-bands.
On stones and shell; dredged.
Arctic, northern and middle Atlantic up to Mediterranean, northern North Sea, Skagerrak, Kattegat, the Belts.