Body short. Thorax somewhat flattened dorsoventrally, posterior part of thorax and anterior part of abdomen tapering, posterior part of abdomen cylindrical. Prostomium with three lobes and usually with two eyespots. Gills in two groups separated by a distance of one or two gills; three gills of each group in a transverse row, fourth gill just behind the middle one of the three; bases of gills on each side fused.
10-30 long, golden and stout chaetae on each side in front of gills, arranged in a fan pointing stiffly forwards. The first parapodium is a tiny achaetous tubercle behind gills. Fourteen thoracic segments with normal notopodia with capillary chaetae, the posterior twelve also with neuropodia with uncini. Twelve abdominal segments with uncini, none with rudimentary notopodia. Thoracic and abdominal uncini with two vertical rows of teeth with 5-7 teeth in each row. Last two thoracic segments and all uncinigerous abdominal segments with a long cirrus above each neuropodium.
Pygidium with two long lateral cirri and a number of long, cirriform papillae.
Up to 45 mm long (bigger in arctic waters).
Thick and loose, straight cylindrical tube of mud and sand lined with a thin secretion.
Living male greenish white, female yellowish pink, gills green, intestine brick red and visible through the transparent body wall. In alcohol pale yellow.
On all types of level bottoms, ranging from silt to coarse sand; from lower eulittoral to about 2000 m; euhaline to mesohaline.
Eastern North Atlantic to Madeira, Mediterranean, North American Atlantic, West Greenland, White Sea, Siberian Arctic, Bering Sea, Sea of Okhotsk, Japan Sea, North American Pacific. East Greenland, Svalbard, Jan Mayen, Iceland, the Faeroes, western Norway, northern Norway, southern North Sea, Skagerrak, Kattegat, the Öresund and the Belts, western Baltic.