Body cup-shaped with ten feathery arms, arm length up to 100 mm but usually less. Colour variable from rosy to deep purple, yellow or orange or mottled and spotted. Up to 20 (rarely 30) short cirri, arising in transverse rows on a low conical centro-dorsal ossicle. The proximal (oral) pinnules are long and modified, with about 35 segments. The distal edges of arm ossicles (brachials) are prominent. The proximal 6-7 joints of the genital pinnules with rather prominent spines at the distal outer corner; beyond these, the pinnule joints diminish rapidly in size. The genital organ is confined to the basal half of the pinnule (A. bifida arm).
This is a free-moving species, attaching temporarily by clawed cirri. It prefers hard bottoms, with shells, hydroids, bryozoans, etc.. The depth range is from about 5-200 m, but this species has exceptionally been recorded from a depth of 450 m. This species is frequently parasitized by Myzostoma, a hermaphrodite polychaete.
In the North Sea this species is found not further south than Northumberland. Elsewhere it is distributed from the Shetland Islands down to Portugal.