Body slender, cylindrical.
Prostomium rhomboid, blunt anteriorly, without an obvious caruncle; the posterior point reaching the middle of the first chaetiger. 4 eyes in a bent line.
Notopodial postchaetal lobes in the segments with gills big and leaf-like, the others small and oval. Anterior parapodia with winged capillaries only. From neuropodium 11-36 and notopodium 18-31 onwards hooks present (A. paucibranchiata-detail).
Gills completely separate from postchaetal lobes, 10-11 pairs, starting at chaetiger 2.
Pygidium with four cirri, the dorsal ones about twice as long as the ventral ones.
Up to 25 mm for 100 segments.
In formaldehyde yellowish to colourless.
Eulittoral to 495 m.
North Sea to Kattegat, North Atlantic, Mediterranean, Black Sea, Argentine.