Body long, cylindrical, anteriorly slightly flattened.
Prostomium rounded, with two dorsolateral nuchal organs and two tentacles (easily lost). Eyes absent.
1st segment without notopodia (sometimes also segments 7-10). The next 10 chaetigers with a cylindrical notopodium supported by an internal acicula; no chaetea. Chaetiger 1 to 7 with cirriform or lanceolate interramal cirrus. Neuropodia of anterior 2 or 3 segments with a triangular subpodial papilla, on chaetiger 4 with a subpodial lobe with 4-6 big papillae, on chaetiger 5 and 6 big, triangular lobes with many small papillae, chaetiger 7 with a big lobe with 6-14 big and conical papillae and chaetigers 8-11 each with a big, finely papillated lobe. Posterior neuropodia conical with several aciculae. Chaetae all variously modified capillaries (A. tullbergi-detail).
Pygidium with two long and one short cirri.
Unknown. Fragments of over 35 segments 12 mm long.
Whitish to yellowish.
Coarse sand, mud and muddy sand, also on seaweeds and Zostera. Upper sublittoral to 360 m.
Arctic, North Pacific, North Atlantic to Mediterranean, northern North Sea to Öresund.