Viper dogfish

dermal denticles with faceted crowns, and numerous light-emitting photophores

bottom trawler Seiryo-Maru in 1986. The first, designated as the holotype, measured 22 cm (8.7 in) long and was collected off Cape Shiono at a depth of 330 m (1,080 ft). The second measured 37 cm (15 in) long and was collected off Hiwasa, Tokushima at a depth of 360 m (1,180 ft). The shark was described as a new species and genus by University of Tokyo researchers Kenji Mochizuki and Fumio Ohe in a 1990 article for the Japanese Journal of Ichthyology. They gave it the name Trigonognathus kabeyai; the generic name is derived from the Greek trigonon ("triangle") and gnathus ("jaw"),^{[citation needed]} while the specific name honors Hiromichi Kabeya, the captain of the Seiryo-Maru.^[3]

rough sharks.^[3] In a 1992 morphological study, Shigeru Shirai and Osamu Okamura placed this species in the squalid subfamily Etmopterinae, which most taxonomists now recognize as the separate family Etmopteridae.^[4][5]

Phylogenetic analyses have variously placed Trigonognathus as closer to one clade or the other or as basal to both, depending on which morphological characters, nuclear DNA markers, and/or mitochondrial DNA markers were used.^[5][6][7]

Early Pliocene (11.6–3.6 Mya).^[9]

tooth rows occur on each side, along with a single tooth row at the upper and lower symphyses (jaw midpoints). The teeth are largest at the symphysis and decline in size towards the corners of the mouth. When the mouth is closed, the upper symphysial tooth overlaps the lower, while the lateral teeth interlock. Five gill slits are seen, with the fifth pair longer than the others.^[2][3]

dermal denticles. Each denticle has a swollen rhombic shape with 10–40 facets on the crown. The viper dogfish is black with distinct darker markings on the underside. These markings contain large numbers of tiny light-producing photophores; more photophores are found sparsely scattered over the rest of the body, as well as in a translucent patch on the upper eyelid. The fins are translucent, and the tip of the caudal fin upper lobe is blackish. The largest known male is 47 cm (19 in) long and weighs 0.43 kg (0.95 lb), and the largest female is 54 cm (21 in) long and weighs 0.76 kg (1.7 lb).^[2][3]

continental slopes and seamounts, at depths of 270–360 m (890–1,180 ft). At night, it has been caught between the surface and a depth of 150 m (490 ft) in water over 1.5 km (0.93 mi) deep. This pattern suggests the viper dogfish performs a diel vertical migration, spending the day in deeper water and rising towards the surface at night; such daily movement may relate to feeding.^[2]

bony fishes, notably lanternfishes in the genera Benthosema and Diaphus, and also takes crustaceans.^[2][3] Its long jaws and slender teeth are adapted for grasping rather than cutting, in contrast to the short jaws and saw-like lower teeth of other dogfish sharks that are suited for excising chunks of meat.^[4] Prey is seized by a rapid extension of the jaws and swallowed whole; the shark can consume fish close to 40% as long as itself.^[2] The viper dogfish is the only dogfish species that lacks a suborbital muscle, which is normally responsible for pulling the jaws forward when biting. Jaw protrusion is instead effected by the hyomandibular bone, which is articulated to the skull in a manner that allows it to swing down and forward. This unique arrangement serves to increase the distance the shark can protrude its jaws, as well as the size of its gape both vertically and horizontally.^[4]

mature sexually at roughly 43 and 52 cm (17 and 20 in) long, respectively.^[2]

purse seines and bottom trawls targeting other species, though what effect, if any, fishing has on its population is unknown. The IUCN has listed it as Least Concern.^[1]