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Troschel, 1857

Large muscular nektonic squids. Mantle in larvae sac-like, in juveniles broadly cup-like, in adults nearly cylindro-conical. Head wider than mantle and may retract into it only in newborn larvae. Fins petaloid in larvae, kidney-shaped in juveniles, in adults longitudinal diamond-shaped, reaching anterior and posterior mantle ends but not fused. Arms short but strong, with 2 rows of suckers, in juveniles relatively longer than in both larvae and adults. Third arms are longest, 4th widened at base. All arms bear wide protective membranes with long cirrus-like trabeculae. Tentacles also short and strong, club widened, with 4 rows of suckers. Fixing apparatus: 2 rows of alternating knobs and suckers along stem. Buccal membrane with 7 lappets, connectives to 4th arms attached ventrally. Funnel cartilage in the form of a tilted "T", with narrow projection in upper and rectangular in lower part. Nuchal cartilage with 2 knobs fitting 2 pits near anterior margin of the mantle. Gladius is like tip of arrow with short stem.
No photophores except probably one on the ink sac in juveniles, lacking in larvae and impreceptible (probably not functional) in adults. The characteristic egg spawn is a mucous stocking-like cylinder 1-2 m long, 10-30 cm in diameter, floating obliquely with one end on the very surface. A string of viscous mucus containing 2 parallel rows of rose-violet eggs approx. 1.5 mm in diameter wound around the cylinder.
Larvae and juveniles also very characteristic: larvae have barrel-like mantle densely speckled by large violet chromatophores (fading after prolonged fixation), small head and protruding eyes (ML <5 mm); juveniles (>10 mm) - widened bases of 4th arms and wide protective membranes on 2nd-3rd arms. ML up to 1 m.
Larvae and juveniles epipelagic, adults rise to very surface at night, descend at day to mesopelagic layers. Living in pairs (male + female) beginning from the late juvenile stage.

Thysanoteuthis rhombus