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Viper dogfish
The viper dogfish or viper shark (''Trigonognathus kabeyai'') is a rare species of dogfish shark in the family Etmopteridae, and the only extant member of its genus. It has been found in the Pacific Ocean off southern Japan, the Bonin Islands, and the Northwestern Hawaiian Islands. This species inhabits upper continental slopes and seamounts. It may migrate vertically, shifting between bottom waters deep during the day and upper waters less than deep at night. A slender black shark reaching in length, the viper dogfish can be recognized by its narrow, triangular jaws and well spaced, fang-like teeth. It also has two spined dorsal fins, dermal denticles with faceted crowns, and numerous light-emitting photophores that are concentrated on its ventral surface.
Feeding mainly on bony fishes, the viper dogfish captures prey by protruding its jaws and impaling them with its teeth. Its impressive gape allows it to swallow relatively large fish whole. The skeletal and muscular structure of its head shows unique features that support this feeding mechanism, which is unlike that of other dogfish sharks. This shark gives birth to live young, which are nourished by yolk during gestation; the litter size is probably fewer than 26 pups. Small numbers of viper dogfish are caught incidentally in purse seines and bottom trawls. The International Union for Conservation of Nature (IUCN) presently lacks sufficient data to assess the conservation status of this species.
==Taxonomy==
The first specimens of the viper dogfish were two immature males caught off southern Japan by the bottom trawler ''Seiryo-Maru'' in 1986. The first, designated as the holotype, measured long and was collected off Cape Shiono at a depth of . The second measured long and was collected off Hiwasa, Tokushima at a depth of . 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"), while the specific name honors Hiromichi Kabeya, the captain of the ''Seiryo-Maru''.〔
Mochizuki and Ohe originally assigned the viper dogfish to the family Squalidae, which at the time was used for all members of the order Squaliformes aside from the bramble and rough sharks.〔 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.〔〔
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