Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Classis: Chondrichthyes
Subclassis: Elasmobranchii
Infraclassis: Euselachii
Division/Cohort: Neoselachii
Subdivision/Subcohort: Selachimorpha
Superordo: Squalomorphii
Ordo: Hexanchiformes
Familia: Hexanchidae
Genera: Heptranchias - Hexanchus - Notorynchus – †Gladioserratus – †Notidanoides - †Notidanodon - †Paraheptranchias - †Pseudonotidanus - †Weltonia
Name
Hexanchidae Gray, 1851
Type genus: Hexanchus Rafinesque, 1810
References
Primary references
Gray, J.E. 1851. List of the specimens of fish in the collection of the British Museum. Part I. Chondropterygii. British Museum (Natural History), London. 160 pp. BHL Reference page.
Vernacular names
Deutsch: Sechskiemerhaie
English: Cow sharks
magyar: Szürkecápafélék, tehéncápafélék
Nederlands: Koehaaien
polski: sześcioszparowate
português: Tubarão de vaca
русский: Cow shark
தமிழ்: பசுச்சுறா
Cow sharks are a shark family, the Hexanchidae, 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]
Description
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 unspecialized, suggesting they may resemble those of primitive shark ancestors. A possible hexanchid tooth is known from the Permian of Japan, making the family a possible extant survivor of the Permian–Triassic extinction.[3]
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] The first pair are not connected across the throat.[5] They range from 1.4 to 5.5 m (4.6 to 18.0 ft) in adult body length.
These cylindrical sharks have a ventral mouth with compressed, comb-like teeth in the lower jaw and smaller, pointed teeth in the upper jaw. They have a short, angular and spinless dorsal fin. The pelvic fins are smaller than the angular pectoral fins. The caudal fin has a notch towards the end.[5]
Biology
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.[6]
Fossil Record
The only fossil records of the cow shark consist of mainly only isolated teeth. Although skeletal remains for this species have been found from the Jurassic time period, these have been very rare and have only been found in the "Late Jurassic lithographic limestones of South Germany, Nusplingen, Solnhofen, and late Cretaceous calcareous sediments of Lebanon." Due to these sparse records some scientists conclude that the cow shark is now a more "diverse and numerous species".[7]
Species
View of the six gill openings of Hexanchus nakamurai
The 37 species of cow shark (five of which are extant), in 10 genera, are:[5][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 howelli 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 vitulus Springer & Waller, 1969[8][9] (atlantic 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 lanceolatus Woodward, 1886
†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 Klug & Kriwet, 2010
†Welcommia bodeuri Cappetta, 1990
†Welcommia cappettai Klug & Kriwet, 2010
†Weltonia Ward, 1979
†Weltonia ancistrodon Arambourg, 1952
†Weltonia burnhamensis Ward, 1979
†Xampylodon Cappetta, Morrison & Adnet, 2019
Xampylodon brotzeni (Siverson, 1995)
Xampylodon dentatus (Woodward, 1886)
Xampylodon loozi (Vincent, 1876)
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References
Froese, Rainer; Pauly, Daniel (eds.). "Family Hexanchidae". FishBase. February 2011 version.
Allen, 45
Burrow, Carole J.; Hovestadt, D. C.; Turner, Sue. "New information on the Devonian shark Mcmurdodus, based on material from western Queensland, Australia". www.academia.edu. Retrieved 2016-06-03.
Matt's, J. & Last P.R. (1998). Paxton, J.R. & Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. p. 61. ISBN 0-12-547665-5.
Compagno, Leonard J. V.; Dando, Marc; Fowler, Sarah L.; Compagno, Leonard; Fowler, Sarah (2005). A field guide to the Sharks of the world. Collins field guide. London: Collins. ISBN 978-0-00-713610-0.
Allen, Thomas B. The Shark Almanac. New York: The Lyons Press, 1999. ISBN 1-55821-582-4
Klug, Stefanie and Kruiwet, Jurgen, “A new Jurassic cow shark (Chondrichthyes, Hexanchiformes) with comments on Jurassic hexanchiform systematics” Swiss Journal of Geosciences, 12 November 2011. https://www.researchgate.net/publication/234060567
"New shark species confirmed: Genetic testing finds a different sixgill shark".
"New species of shark discovered through genetic testing".
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