(O.F. Müller, 1776)
Body with a central disc of up to 10 mm in diameter and 5 fine and coiled arms of about 10 times that length; coloured reddish- or greyish-brown.
Disc covered with fine scales on dorsal side only, the primary plates are indistinguishable. The radial shields are separated, but may join at the base (A. filiformis disc).
Dorsal arm plates are transverse oval, the ventral arm plates more or less square. There are 5-7 arm spines per segment. Tube foot pores are not covered by tentacle scales (A. filiformis arm).
Mouth shields are rounded pentagons. Paired infradental papillae on top of the jaws, one spine-like outer mouth papilla on each side of jaws, not contiguous with the infradental papillae. Two pairs of tube-feet within the mouth (A. filiformis mouth).
This species is found on muddy sand where it burrows about 50 mm into the bottom, from depths of about 5-1200 metres.
In the North Sea, this species is found from the North down to the coast of Northumberland, the Dogger bank and Helgoland. Elsewhere it is distributed from the Trondhjemfjord, to the Sound in Scandinavian seas, and to the Mediterranean. It does not occur at the Atlantic coasts of N. America or at Greenland.