The average size of adult H. pfefferi is in mantlelength. The body consists of a large funnel with small paddle-like fins. They have small tentacles above their eyes. The funnel does not have valves, but contains a dorsal pad with three papillae as organs. Paddle-shaped fins are attached to a part of the gladius. H. pfefferi has a single ocularphotophore and does not have photophores at its arm tips.