Body long and slender; thorax cylindrical, abdomen tapering towards the pygidium.
Prostomium with two groups of eyespots. Gills in two nearly contiguous groups; three gills of each group in a transverse row, the fourth one behind the innermost one of the three.
Chaetae of segment 3 long and fine, 12-14 on each side. Fifteen thoracic segments with notopodia with capillary chaetae; first pair of notopodia very small and often overlooked, 11th pair elevated, but not transformed, with chaetae with denticulate tips and connected by a low dermal ridge bearing a transverse band of cilia. Twelve thoracic and thirteen abdominal uncinigerous segments. Thoracic uncini with two vertical rows of teeth with six teeth in each row, abdominal uncini with three vertical rows of teeth with five teeth in each row (A. gracilis-detail).
Pygidium without cirri.
Up to 47 mm.
A thin layer of secretion encrusted with silt and clay.
Living animal yellow to yellowish pink with a faint blue iridescence, the band of cilia highly iridescent. In alcohol yellowish, often glossy.
Mainly on silt and mixed bottoms, rarely on pure sand; from the upper sublittoral to about 3000 m; euhaline to polyhaline (temporarily also mesohaline).
Eastern North Atlantic, Canadian Atlantic, West Greenland, Siberian Arctic, North American Pacific, Yellow Sea. Iceland, Jan Mayen, Barents Sea, entire Norwegian coast, North Sea, Skagerrak, Kattegat, Swedish west coast, Öresund.