Body short and plump, tapering towards pygidium.
Upper lip low, but distinct, folded. Lower lip inconspicuous. Tentacular lobe laterally and posteriorly enclosing the mouth and tentacles. Peristomium ventrally forming a big, protrusive proboscis.
Proboscis distally with numerous conspicuous papillae, more or less in longitudinal rows, proximally with longitudinal folds.
Tentacles numerous, fine and short. Gills on segments 2-4. Each of the three pairs of gills consisting of a number of free filaments, no stems discernible. Seventeen thoracic segments with notopodia with capillary chaetae (starting on segment 4), the posterior sixteen also with neuropodia with uncini. About ten ventral shields more or less developed (starting on segment 4). Thoracic uncini on low tori, abdominal uncini on protruding, flat pinnules with more or less developed leaf-like dorsal cirri (A. proboscidea-detail).
Pygidium without appendages.
Up to 82 mm.
Very loose, uniformly encrusted with a thick layer of mud.
In life yellowish pink to red, gills bright red, tentacles whitish. In alcohol yellowish grey.
Mainly on soft bottoms, pure or sand-mixed silt; rarely on clay or among benthic plants; upper sublittoral to about 3000 m; euhaline to mesohaline.
Antarctic, Subantarctic, Arctic, North Pacific, North Atlantic, northern North Sea, Skagerrak, Kattegat, Big Belt, Öresund and Baltic to Mecklenburg.