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Cow sharks are a family, the Hexanchidae, of sharks characterized by an additional pair or pairs of gill slits. There are 37 species within the 10 genera Gladioserratus, ''Heptranchias'', ''Hexanchus'', ''Notidanodon'', ''Notorynchus'', ''Pachyhexanchus'', ''Paraheptranchias'', ''Pseudonotidanus'', ''Welcommia'', and ''Weltonia''.〔Allen, 45〕〔Compagno, L., Dando, M. and Fowler, S. ''Sharks of the World''. Princeton Field Guides ISBN 0-691-12072-2〕 Cow sharks are considered the most primitive of all the sharks, as their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialised, suggesting they may resemble those of primitive shark ancestors. Their most distinctive feature, however, is the presence of a sixth, and, in two genera, a seventh, gill slit, in contrast to the five found in all other sharks. They range from in adult body length. Cow sharks are ovoviviparous, with the mother retaining the egg cases in her body until they hatch. They feed on relatively large fish of all kinds, including other sharks, as well as on crustaceans and carrion.〔Allen, Thomas B. ''The Shark Almanac''. New York: The Lyons Press, 1999. ISBN 1-55821-582-4〕 == Species == The 37 species of cow shark, in 10 genera, are: * †''Gladioserratus'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 * * †''Gladioserratus aptiensis'' Pictet, 1864 * * †''Gladioserratus dentatus'' Guinot, Cappetta & Adnet, 2014 * * †''Gladioserratus magnus'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 * ''Heptranchias'' Rafinesque, 1810 * * ''Heptranchias perlo'' (Bonnaterre, 1788) (Sharpnose sevengill shark) * * †''Heptranchias ezoensis'' Applegate & Uyeno, 1968 * * †''Heptranchias howellii'' Reed, 1946 * * †''Heptranchias karagalensis'' Kozlov in Zhelezko & Kozlov, 1999 * * †''Heptranchias tenuidens'' Leriche, 1938 * ''Hexanchus'' Rafinesque, 1810 * * ''Hexanchus griseus'' (Bonnaterre, 1788) (Bluntnose sixgill shark) * * ''Hexanchus nakamurai'' Teng, 1962 (Bigeyed sixgill shark) * * †''Hexanchus agassizi'' Cappetta, 1976 * * †''Hexanchus andersoni'' Jordan, 1907 * * †''Hexanchus casieri'' Kozlov, 1999 * * †''Hexanchus collinsonae'' Ward, 1979 * * †''Hexanchus gracilis'' Davis, 1887 * * †''Hexanchus hookeri'' Ward, 1979 * * †''Hexanchus microdon'' Agassiz, 1843 * * †''Hexanchus tusbairicus'' Kozlov in Zhelezko & Kozlov, 1999 * †''Notidanodon'' Cappetta, 1975 * * †''Notidanodon brotzeni'' Siverson, 1995 * * †''Notidanodon dentatus'' Woodward, 1886 * * †''Notidanodon lanceolatus'' Woodward, 1886 * * †''Notidanodon loozi'' Vincent, 1876 * * †''Notidanodon pectinatus'' Agassiz, 1843 * ''Notorynchus'' Ayres, 1855 * * ''Notorynchus cepedianus'' (Péron, 1807) (Broadnose sevengill shark) * * †''Notorynchus borealus'' Jordan & Hannibal, 1923 * * †''Notorynchus kempi'' Ward, 1979 * * †''Notorynchus lawleyi'' Cigala Fulgosi, 1983 * * †''Notorynchus primigenius'' Agassiz, 1843 * * †''Notorynchus serratissimus'' Agassiz, 1843 * * †''Notorynchus subrecurvus'' Oppenheimer, 1907 * †''Pachyhexanchus'' Cappetta, 1990 * * †''Pachyhexanchus pockrandti'' Ward & Thies, 1987 * †''Paraheptranchias'' Pfeil, 1981 * * †''Paraheptranchias repens'' Probst, 1879 * †''Pseudonotidanus'' Underwood & Ward, 2004 * * †''Pseudonotidanus semirugosus'' Underwood & Ward, 2004 * †''Welcommia'' Cappetta, 1990 * * †''Welcommia bodeuri'' Cappetta, 1990 * * †''Welcommia cappettai'' Klug & Kriwet, 2010 * †''Weltonia'' Ward, 1979 * * †''Weltonia ancistrodon'' Arambourg, 1952 * * †''Weltonia burnhamensis'' Ward, 1979 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cow shark」の詳細全文を読む スポンサード リンク
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