Mantle narrow, cylindrical in anterior, conical in posterior half. Head can be wholly retracted into mantle. Fins tongue-like in larvae, heart-shaped in juveniles, diamond-shaped with short tapering tail in adults. Arms rather short, strong. Only 1st and 2nd arms in early larvae, 3rd appearing later only at ML approx. 5 mm. Tentacles long. Larval tentacular club with 4 rather irregular rows of suckers, 2 central rows transformed later into hooks, those of the ventral row first (at ML approx. 12-15 mm). In adults 19-23 hooks, marginal suckers absent in juveniles. Nuchal folds on head well developed. Gladius very narrow, with strong longitudinal dorsal rib easily visible from dorsal, with acute chitinous needle behind, directed diagonally dorsally and protruding through skin upon fixation in larvae. Skin smooth.
Larvae almost transparent, with sparse chromatophores, covering predominantly dorsal mantle side in juveniles and adults, red-brown. One elongate photophore on ventral side of eyeball, 2 near the hindgut (one small near anus, one large and round in an arch-like bend of the gut near its beginning, developed at ML approx. 9-11 mm). Degenerating mature females described as Chaunoteuthis mollis Appellöf, 1890. Larvae easily distinguishable by acute needle protruding from posterior end, light in color, and usually with head retracted. ML up to 17 cm.
Of the approximately 5 species known in genus, only Onychoteuthis banksii, a species complex represented by some local forms, is known from the Atlantic. Juveniles may leap out of the water at night; adults widely eurybathic.