Bigfin reef squid

Like other members of the genus Sepioteuthis, bigfin reef squids are easy to distinguish from other squids in that they possess thick and muscular oval fins that extend around almost the entire mantle. The fins extend about 83 to 97% of the mantle length and are 67 to 70% of the mantle length in width. Because of these fins, bigfin reef squids are sometimes mistaken for cuttlefish, a fact reflected by their scientific names. A narrow blue or white line is visible at the point of attachment of the fins to the mantle. A fleshy ridge is also present where the fins meet at the back of the squid. The mantles of bigfin reef squids are cylindrical, tapering to a blunt cone at the posterior. The mantle is usually 4 to 33 cm (1.6 to 13.0 in) long in males and 3.8 to 25.6 cm (1.5 to 10.1 in) long in females. Both sexes can reach a maximum mantle length of 38 cm (15 in). Adult males weigh 403.5 to 1,415 g (0.890 to 3.120 lb), while adult females are 165 to 1,046 g (0.364 to 2.306 lb). Both sexes can attain a maximum documented weight of 1.8 kg (4.0 lb). The forward margin of the mantle on the ventral side is concave. Their eyes are large and covered entirely by a transparent secondary cornea. They are greenish at the base. A pair of prominent ridges (olfactory crests) are present on the ventral surface of the head at the rear edge of the eyes. The mouth area is supported by seven triangular flaps (buccal lappets), each with 0 to 7 suckers of less than 0.2 mm in diameter and 18 to 25 teeth. The strong, curved, and short beaks (rostra) are mostly black to dark brown. The radula has seven rows of teeth. The spermatophores of males are about 4.5 mm (0.18 in) long and 0.15 mm wide.