Prostomium broadly rounded, with three lobes and two simple eyespots. Gills in two widely separated groups connected by a dermal ridge. First three gills in each group in a transverse row, the fourth one just behind the middle one of the three.
6-8 stout, short chaetae with pointed tips on each side in front of the gills; may be covered by gills.
Fourteen thoracic segments with normal notopodia with chaetae, posterior twelve ones also with neuropodia with uncini. Twelve uncinigerous abdominal segments, the anteriormost three with rudimentary notopodia. First two abdominal neuropodia short, wartlike, following ones stalked and flattened, each with a very short cirrus at the dorsal margin. Thoracic chaetae of several types, including geniculate ones and subdistally flattened, sickleshaped ones. Uncini pectinate, thoracic ones with two rows of secondary teeth, abdominal ones with irregularly arranged secondary teeth (A. falcata-detail).
Pygidium with a pair of long cirri and a number of round or conical papillae.
Up to 18 mm long.
On mixed bottoms in depths between 30 and 90 m. There are very few records of the species.
Swedish west coast, Skagerrak, Kattegat, Norway, North Sea, Irish Sea.