Body long, rather soft. Tentacles numerous, short or moderately long. Upper lip low, curving around and dorsally and laterally covering the mouth. Many eyspots. Two pairs of gills (on segments 2 and 3), dichotomous branched with long stems. Anterior gills much longer than the posterior ones. No lateral lobes. 13-17 ventral shields. Notopodial chaetae from segment 4. 17-18 chaetigerous thoracic segments. Uncinigerous tori from segment 5. Uncini in double rows on segments 11-20. Pygidium with smooth edge. Notopodial chaetae smooth, with narrow brims. Uncini with one big and several smaller teeth.
Up to 70 mm for 70 segments.
A thin, transparent layer of secretion encrusted with sand grains and algal fragments.
In life orange red, dorsally with white spots, tentacles violet, gills red. In alcohol pale yellow.
On hard bottoms, often with some sand and mud, or among stones, shells, algae or hydroids; upper sublittoral to a depth of about 700 m.
North Atlantic to Senegal, Mediterranean, White Sea, Siberian Arctic, Canadian and Alaskan Arctic, Red Sea, South Africa; East Greenland, Iceland, The Faeroes, Jan Mayen, Svalbard, southern Norway, North Sea, east coast of Great Britain, Swedish west coast, Kattegat, the Öresund and the Belts.