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Broadnose sevengill shark
The broadnose sevengill shark (''Notorynchus cepedianus'') is the only extant member of the genus ''Notorynchus'', in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark. This shark has a large, thick body, with a broad head and blunt snout. The top jaw has jagged, cusped teeth and the bottom jaw has comb-shaped teeth. Its single dorsal fin is set far back along the spine towards the caudal fin, and is behind the pelvic fins. In this shark the upper caudal fin is much longer than the lower, and is slightly notched near the tip. Like many sharks, this sevengill is counter-shaded. Its dorsal surface is silver-gray to brown in order to blend with the dark water and substrate when viewed from above. In counter to this, its ventral surface is very pale, blending with the sunlit water when viewed from below. The body and fins are covered in a scattering of small black & white spots. In juveniles, their fins often have white margins.
It is also known as sevengill shark or simply sevengill and was formerly known as cow shark and mud shark; it is called sevengill due to its seven gill slits. Because of this, it was listed along with the sharpnose sevengill shark (''Heptranchias perlo'') by Guinness World Records as having the most gill slits. It is similar to the sharpnose sevengill shark but the latter has a pointed snout and lacks spots on its dorsal surface. The sevengill species are also related to ancient sharks as fossils from the Jurassic Period (200 to 145 million years ago) also had seven gills. As recent as the 1930s and 1940s, the shark was targeted by fisheries along the coast of California and, once the commercial fishery receded, recreational fishing of the shark started in the 1980s and 1990s.〔
==Description==
The length at birth is 40–45 cm (16-18 inches) while the ''mature male length'' is 150 cm (1.5 meters) and ''mature female length'' is around 220 cm (2.2 m). The maximum length found is 2.9 m. The shark is large and active and has a large head but small eyes and snout. The shark has one dorsal fin at the back of the body that spans from the insertion to the tops of the pelvic fins.〔
The broadnose sevengill shark is also known as sevengill shark or simply sevengill and was formerly known as cow shark and mud shark; it is called sevengill due to its seven gill slits. Because of this, it was listed along with the sharpnose sevengill shark by Guinness World Records as having the most gill slits.〔 It is similar to the sharpnose sevengill shark but the latter has a pointed snout and lacks spots on its dorsal surface.〔 The sevengill species are also related to ancient sharks as fossils from the Jurassic Period (200 to 145 million years ago) also had seven gills.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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