While most seasnails can be easily recognized by
their characteristic adhesive disc, it is absent from this species. Its body shape
is typical of snailfish, long and tapering, with a large head, dorsal and anal
fins that run the length of the body, and a much reduced caudal fin. Its pectoral
fins are unusual in that they have two lobes, the lower consisting of 3 or 4 separate
rays. The mouth is horizontal with broad bands of teeth that are used to crush
amphipods, snails and crustaceans. Overall, the body colour is black, fading to
a dark grey towards the posterior end of the fish. Black seasnails reach a maximum
length of 25 cm.
This species is found in the north Atlantic from off west Greenland to Baffin
Bay in cold, deep water and individuals have been hauled up from as deep as 4000
m! Because of their deepwater habitat, not much is known about their biology except
that spawning likely takes place in the summer and females produce over 400 eggs.