Body elliptical. Dorsal surface smooth, ventral surface densely papillate. Prostomium round, very small with a short median anterior antenna, two pairs of eyespots, each pair on a raised area, a pair of large palps, and a large papillate facial tubercle which lies between the bases of the palps and above the mouth. First segment well developed with a pair of dorsal and ventral tentacular cirri and numerous chaetae: a dorsal group of long fine capillaries and a ventral group of shorter stout capillaries.
Scales overlap, covering the body. They occur on segments 1, 3, 4 and 6 then alternately to the 24th, and then on segments 29 and 30. The first and second pair of scales are round, attached in the middle, the rest oval to rectangular attached by the stalk and also along the dorsal surface of the notopodium, the outer margins notched and all surfaces smooth.
Notopodia are irregular mounds obscured by numerous chaetae. Notopodial chaetae of three kinds: 1) an upper group of extremely long fine capillaries, that form the felt covering the scales; 2) numerous long, fine iridescent capillaries, and 3) very stout spines. Neuropodia well developed with chaetae in horizontal rows. Neuropodial chaetae of three or four kinds: 1) stout spines in neat rows; 2) stout capillaries laterally spinose on the 1st, 2nd, and some posterior parapodia; 3) fine capillaries with spines on posterior parapodia; 4) chaetae with brush-like tips present in juveniles (A. aculeata-detail).
Up to 200 mm for 40 chaetigers.
Body and scales pale grey/white, felt brown due to presence of mud and detritus, some notopodial chaetae iridescent.
Sublittoral to over 1000 m, on muddy bottoms.
Northern hemisphere, North Atlantic, Mediterranean, North Sea, Skagerrak, Belts and Öresund.