O.F. Müller, 1771 in 1776
Body long; thorax dorsally convex, laterally and ventrally flattened; abdomen tapering.
Tentacles numerous, very long. Upper lip low, covering the mouth dorsally and laterally. Three pairs of gills (on segments 2-4), each gill consisting of numerous free filaments arising from a very short, wartlike stem; the filaments contract spirally. Distinct lateral lobes on segments 2-4.
Notopodial chaetae from segment 4. Seventeen thoracic segments with finely denticulate capillary chaetae with fine teeth at the tip on notopodia. Prominent uncinigerous tori on neuropodia from the 2nd chaetiger, long on thorax, short on abdomen. Uncini in double rows on segments 11-20, large (A. cirrata-detail).
Pygidium without appendages.
Up to 200 mm for 95 chaetigers.
A thin layer of secretion encrusted with a thick layer of mud and a few sand grains.
In life pinkish grey to brown, tentacles with brown spots, gills red. In alcohol large and medium specimens brown, small ones yellowish.
On mud, clay, sand and mixed bottoms, and also on hard substrata, such as coralline bottoms, Sabellaria reefs, and among ascidians; lower eulittoral to depths below 2700 m; euhaline to mesohaline.
Eastern North Atlantic to the Azores, Mediterranean, North American Atlantic, West Greenland, Canadian and Alaskan Arctic, Siberian Arctic, Bering Sea, Sea of Okhotsk, Japan Sea, North American Pacific. East Greenland, Svalbard, Barents Sea, Iceland, the Faeroes, Shetland, entire Norwegian coast, northern North Sea, Skagerrak, Kattegat, the Öresund and the Belts, western Baltic, east coast of Great Britain.