A small, cigar-shaped body. Two very small, spineless dorsal fins. Origin of first dorsal fin in front of the pelvic fins. The space between the two dorsal fins is more than twice the base of the first dorsal fin. Large eyes, more terminally positioned such that a frontal view looks like a "face". (Contrary to this, requiem sharks have their eyes on the side of their heads). Bulbous snout. Nearly symmetrical caudal fin. No anal fin.
Coloration
Dark brown with white ventral surface. Dark collar-marking over the branchial region. Luminous organs that cover the entire lower surface of the trunk, producing a greenish light.
Distribution
Probably worldwide in tropical waters. Western Atlantic: Bahamas, southern Brazil to Cape Verde Islands, southern Angola to South Africa. Mauritius to New Guinea and western Australia. Japan to Hawaiian Islands, and Galapagos.
Biology
Lives in epipelagic and bathypelagic waters between 80 m and about 3500 m, but can come to the surface at night during diurnal migrations. This species possesses very strong teeth (sawlike dentition) and jaws, and sutorial lips that allow it to attach on bigger animals and bite chunks out of them (e.g. on dolphins, marlins, megamouth sharks and others). The wounds are circle-shaped,as caused by the twisting shark, and give the shark its name. They can live as ectoparasites.
Diet
Mainly cephalopods, but can live as ectoparasites.
Size
Average size between 30 cm and 40 cm, maximum total length about 50 cm.
Reproduction
Unknown, though most likely aplacental viviparous (ovoviviparous). Litter size between 6 and 7 pups. Males reach sexual maturity with about 38 cm, females with about 40 cm.