The black seasnail (Paraliparis bathybius) is a species of fish in the family Liparidae (snailfish).
The black seasnail has a long and tapering body (maximum ), black and grey in colour, with large head, dorsal and anal fins that run the length of the body, and a much reduced caudal fin, although it has no adhesive disc, unlike other snailfish. The pectoral fins have two lobes, the lower having 3âÂÂ4 rays.
The black seasnail is bathydemersal, living in the Arctic Ocean and North Atlantic Ocean at depths of .
It feeds on amphipods, gastropods and mysids. It spawns in summer, producing up to 400 eggs up to in diameter.