Body long and cylindrical.
Prostomium anteriorly broadly rounded, ocelli absent. Nuchal slits relatively short, weakly bent.
The eight anterior segments with glandular bands, the following segments with glandular areas around parapodia; on the posterior part the glandular areas are large.
21 chaetigers. The notopodia bear capillary chaetae with feathery tips. The three first segments with ventral spines, following segments with a row of hooks. One posterior segment without chaetae (P. borealis-detail).
Pygidium strongly asymmetrical, dorsally very short and ventrally much longer, without cirri.
Up to 44-73 mm for 21 chaetigers.
Flattened, fixed to stones or muscle shells, strongly meandering, with crust of sand.
Anterior body half to only 3rd chaetiger more or less weakly with red-brown pigmentation, following segments or also posterior segments irregularly spotted red.
In mud mixed with stones; from sublittoral down to about 1700 m deep.
Arctic, North Pacific, North Atlantic, northern North Sea, Skagerrak, Kattegat to middle Öresund.