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(Steenstrup, 1855)

Mantle cylindro-conical, narrowing behind, rather wide in larvae, robust in adults, narrow in juveniles. Head not retractable. Fin broadly diamond-shaped, not tapering into tail. Fin width 3/4 ML or more. Arm ends not tapering. Ventral protective membranes on 3rd arms widened but not forming a wide triangular lobe, width approximately equal to arm width. Tentacles rather narrow but strong. Rings of large club suckers with 4 long teeth located crosswise, others smaller. Fixing apparatus with knobs and suckers; not more than 2 small dentate suckers proximal to first knob on tentacular stem. Funnel pit with foveola, longitudinal ridges and side pockets. Funnel and mantle cartilages not fused.
Many small photophores dispersed under skin of mantle, head, and 4th arms, grouped to form large oval, orange luminous spot on dorsal mantle muscles in its anterior part; one eyeball photophore, two nearly equal gut photophores, near anus and near beginning of gut. Dorsal photophore developed only before sexual maturation, at ML approx. 8-9 cm. No silvery reflecting cigar-like stripe along ventral mantle, wide dark stripe along dorsal midline not bordered by thin ones. ML up to 65 cm.
Larvae: proboscis long, thin, usually not less than 2/3 ML and 2-3 times as long as arms; lateral suckers on tip larger than others. Proboscis beginning to split at ML approx. 4.5-5 mm, finishing at 9-10 mm. Third and 4th arm pairs developed at ML approx. 1.5-1.7 and 2.0-2.5 mm, respectively. Mantle in larvae barrel-shaped, in juveniles narrow, pencil-like. Head not retractable into mantle. Eyeball photophores developed at ML approx. 3-3.5 mm, anterior (anal) and posterior gut photophores at 3-4 and 5-5.5 mm, respectively. Mantle in larvae with dispersed large brown chromatophores, in juveniles with crimson and brown chromatophores.
One species in the Atlantic Ocean. Foraging range between approx. 34-36°N and S, reproductive range between approx. 22°N and 20°S (off Namibia southern boundary of reproductive range near 15-18°S, of foraging range usually near 23-24°S). Epipelagic oceanic species, very common and potentially commercial.

Sthenoteuthis pteropus