 The viper dogfish or viper shark ( Trigonognathus <unk> ) 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 270 – 360 m ( 890 – 1 @,@ 180 ft ) deep during the day and upper waters less than 150 m ( 490 ft ) deep at night . A slender , black shark reaching 54 cm ( 21 in ) 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 concentrated on its ventral surface . 
