Brachioteuthis riisei

(Steenstrup, 1882)

Mantle narrow, cylindrical or becoming conical ahead of the end of the anterior fin. Head narrow, but not retractable into mantle. Neck in larvae long, sometimes grotesquely so, eyes below midline of head. Fins petaloid in larvae, diamond-shaped in juveniles and adults, straight or weakly tapering behind, fin length less than width, not exceeding half ML. Arms short, with 2 rows of suckers. Tentacles in larvae and juveniles much longer than arms, club wide, with 2-4 rows of rather large suckers in carpal, 6-8 rows of knobs in distal part, in adults relatively shorter, with many rows of small suckers in carpal, 4-6 rows of larger ones in distal part. Transition from larval to adult pattern at ML >10 mm. Fixing apparatus: 2 rows of small suckers along stem. Buccal membrane with 7 lappets, connectives to 4th arms attached ventrally. Funnel cartilage straight, simple. Gladius with thin, very long rachis and narrow vane. In some forms a photophore on ventral eyeball. Eggs oval, 1.2-1.5 mm in greater axis.
Larvae and juveniles easily distinguishable by narrow head, long neck, and many rows of carpal club suckers, light in color, with sparse chromatophores. Juvenile appearance at ML approx. 15 mm. ML up to 17 cm in Antarctic, up to 8 cm in other areas.
A complex of species with unclear relationships. Brachioteuthis riisei (Steenstrup, 1882) is supposedly a North Atlantic and southern circumglobal bi-temperate species with a tropical-subtropical circumglobal counterpart [Brachioteuthis behni (Steenstrup, 1882)] and another, as yet unnamed, circum-Antarctic species. Eye photophores are reported in adult B. riisei but not in two other. The larvae of B. behni are characterised by a very long neck and eyes directed at right angles to the longitudinal head axis; those of B. riisei and of the Antarctic form by a moderately long neck and eyes directed anteriorly at acute angles to the longitudinal head axis. Another species in the South Atlantic - Brachioteuthis picta Chun, 1910, has a photophore ventrally on the eyeball.