Mantle elongate, smooth. Head wider than mantle. Eyes usually large, protruding in larvae. Fin wide, heart-shaped or oval, both halves fused along dorsal side of mantle. In some species fin continues beyond mantle end. Arms subequal in larvae, in adults 4th pair much longer than 1st-3rd. Tentacles in larvae with 4-6 suckers, in adults with more than 15-20 rows of suckers along almost entire circumference of club. Approximately 10 species, about 7 in the South Atlantic. Mostly bathypelagic, some also bathyal, larvae predominantly mesopelagic.
Larvae distinguishable by long tail and club with minute suckers. Larvae of most species remain undescribed.