shark rare species shark family extant member genus found pacific_ocean southern japan species inhabits upper continental slopes migrate vertically shifting waters deep day upper waters deep night slender black shark reaching length recognized narrow triangular jaws spaced like teeth dorsal fins dermal denticles crowns numerous light concentrated ventral surface feeding mainly bony fishes captures prey protruding jaws teeth impressive allows swallow relatively large fish skeletal muscular structure head shows unique features support feeding mechanism unlike sharks shark gives birth live young yolk gestation litter size probably fewer pups small numbers caught incidentally purse iucn presently lacks sufficient data assess conservation status species taxonomy specimens immature males caught southern japan designated measured long collected depth second measured long collected depth shark described new species genus researchers article gave generic derived greek triangle jaw specific honors captain originally assigned family time members order aside rough sharks morphological study placed species subfamily recognize separate family phylogeny evolution position uncertain morphological molecular phylogenetic data generally support subdivision consisting consisting phylogenetic analyses variously placed closer clade basal depending morphological characters nuclear dna markers mitochondrial dna markers based molecular clock thought originated million years ago larger evolutionary radiation genera genus represented time period extinct species teeth recovered age strata southwestern france fossil teeth virtually identical modern known northeastern venezuela dates late early description slender cylindrical body moderately flattened head short blunt snout large oval eyes narrow elliptical nostrils nearly vertical slits jaws long narrowly triangular head teeth like widely spaced anterior teeth upper seven lower tooth rows occur single tooth row upper lower jaw teeth largest decline size corners mouth mouth closed upper tooth overlaps lower lateral teeth gill slits seen fifth pair longer fins small thin pectoral fins rounded lobe like dorsal fins positioned pectoral pelvic fins dorsal fin bears slightly spine second dorsal spine longer anal fin absent caudal lacks upper lobe caudal fin larger lower notch trailing margin skin excluding fins densely covered irregularly arranged dermal denticles swollen shape crown black distinct darker markings underside markings contain large numbers tiny light producing found sparsely scattered rest body translucent patch upper fins translucent tip caudal fin upper lobe largest known male long weighs largest female long weighs distribution habitat specimens collected relatively small area northwestern pacific_ocean japan number specimens recovered predatory fishes caught specimen caught located northwest northwestern day species caught close upper reaches continental slopes depths night caught surface depth water deep pattern suggests performs vertical migration spending day deeper water rising surface night daily movement relate feeding biology ecology feeds primarily bony fishes notably genera takes crustaceans long jaws slender teeth adapted cutting contrast short jaws saw like lower teeth sharks suited meat prey seized rapid extension jaws shark consume fish close long species lacks muscle normally responsible pulling jaws forward biting jaw instead effected bone articulated skull manner allows swing forward unique arrangement serves increase distance shark jaws size vertically horizontally known predators include like members family species viviparous developing embryos sustained term yolk adult females functional functional recorded female specimens contained mature related black number mature female slightly greater number resulting embryos suggests litter size males females mature sexually roughly long respectively human interactions economic value caught commercial purse targeting species effect fishing population unknown result iucn listed
Viper dogfish