Cow shark

Cow sharks Temporal range: Upper Jurassic–Recent PreЄ Є O S D C P T J K Pg N [1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Superorder:	Selachimorpha
Order:	Hexanchiformes
Family:	Hexanchidae J. E. Gray, 1851
Genera
See text

Cow sharks are a family, the Hexanchidae, of sharks characterized by an additional pair or pairs of gill slits. Its 37 species are placed within the 10 genera Gladioserratus, Heptranchias, Hexanchus, Notidanodon, Notorynchus, Pachyhexanchus, Paraheptranchias, Pseudonotidanus, Welcommia, and Weltonia.^[2][3]

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.^[4] They range from 1.4 to 5.5 m (4.6 to 18.0 ft) 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.^[5]

Species

The 37 species of cow shark, in 10 genera, are:^[1]

• †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

View of the six gill openings of Hexanchus nakamurai

References

1. Froese, Rainer, and Daniel Pauly, eds. (2011). "Hexanchidae" in FishBase. February 2011 version.
2. Allen, 45
3. Compagno, L., Dando, M. and Fowler, S. Sharks of the World. Princeton Field Guides ISBN 0-691-12072-2
4. Matt's, J. & Last P.R. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. p. 61. ISBN 0-12-547665-5.
5. Allen, Thomas B. The Shark Almanac. New York: The Lyons Press, 1999. ISBN 1-55821-582-4

External links

• ReefQuest Centre: Order Hexanchiformes: Cow Sharks