(Linné, 1758)
An internal calcareous shell in the form of a decoiled (as in a ram's horn) spiral, functioning as a float, on posterior end of body in sagittal plane under thin skin, consisting of isolated chambers connected by a hollow tube (siphuncle). Number of chambers from 3 (in smallest known juvenile) to 40 (in adults). Mantle thick, not fused with head. Eyes large, protruding, covered by transparent skin. Fins small, kidney-shaped, near very end of body oblique to longitudinal body axis. Large round photophore between fins at end of body. Bases of all arms joined by membrane. Arms with 2 rows of suckers. Tentacles retractable with thin stem and small widened club. Club suckers in 16 rows. Color creamy-white with maroon-red. Life position vertical, head down. Development almost direct. Egg size 1.5-1.7 mm, ML of smallest juvenile 1.5 mm; ML of adults up to 5 cm.
Occurs mainly over continental and insular slopes and in the open ocean not far from the slope. Range disjunct and associated with closed circulations of intermediate water masses. In the South Atlantic found only off Namibia and Western Cape, probably expatriated from the SW Indian Ocean, where a known population exists. Spawns on the bottom at bathyal depths. Early juveniles ascend to midwater. Late juveniles and immature subadults migrate from approx. 100-300 m at night to 500-1000 m at day.