Body long, broad behind the gills and tapering towards the pygidium. Characteristic longitudinal, dorsolateral ridges on segments 3-5. Prostomium with three lobes, without glandular ridges, with eyespots.
Gills in two groups separated by a distance of about one base of a gill and connected by a membrane of varying height; three gills in each group in an oblique row slanting posteriorly towards the middorsum, the fourth gill in front of the middle one of the three.
A pair of stout dorsal hooks behind the gills. An anteriorly orientated serrated brim with sharp points across the dorsum behind the hooks. The points of the serrated brim sharp. Segments 3-6 with fine neuropodial spines. Sixteen thoracic segments with notopodia with capillary chaetae (those of segment 5 very small), the posterior 14 also with neuropodia with uncini. About 50 uncinigerous abdominal segments. Pygidium with inconspicuous papillae. Ventral chaetae of segments 3-6 acicular, from segment 7 and throughout thorax pectinate uncini with 1 row of 4 teeth; abdominal uncini with 1 or more rows of four teeth.
Up to 50 mm for 75 segments.
Characteristic, long, tapering posteriorly, encrusted with a more or less thick layer of clay and usually with shell fragments transversely arranged and protruding out of the clay.
In alcohol yellowish or pink.
Eastern North Atlantic, Arctic, North Sea, Skagerrak.