Hexanchiformes

Hexanchiformes
The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.
Description
Hexanchiform sharks have one spineless dorsal fin located over or behind the pelvic fins and one anal fin. The vertebral column extends into the long dorsal lobe of the caudal fin, while the ventral lobe is either small or absent. They have either six or seven gill slits, located in front of the pectoral fins. They have a large mouth, with eyes on either side of the head. The spiracles are small and located well above and behind the eyes. The eyes have no nictitating membrane. Shark teeth similar to modern hexanchids are known from Devonian deposits in Antarctica and Australia, as well as Permian deposits in Japan. If these are in fact hexanchids, this may be the only extant order of elasmobranchs to have survived the Permian extinction (and by extension, the oldest extant order of elasmobranchs).
The frilled sharks of the genus Chlamydoselachus are very different from the cow sharks, and have been proposed to be moved to a distinct order, Chlamydoselachiformes.
Distribution
Species are widespread and found across most of the world. They are most common in cold deep water in the tropics, but are also found closer to the shore in more temperate regions.
Classification
Living species
Family Chlamydoselachidae Garman 1884 (frilled sharks)
Chlamydoselachus Garman, 1884
Chlamydoselachus africana Ebert & Compagno, 2009 (Southern African frilled shark)
Chlamydoselachus anguineus Garman, 1884 (frilled shark)
Family Hexanchidae J. E. Gray 1851 (cow sharks)
Heptranchias Rafinesque, 1810
Heptranchias perlo (Bonnaterre, 1788) (sharpnose sevengill shark)
Hexanchus Rafinesque, 1810
Hexanchus griseus (Bonnaterre, 1788) (bluntnose sixgill shark)
Hexanchus nakamurai Teng, 1962 (bigeyed sixgill shark)
Hexanchus vitulus Daly-Engel, 2018 (Atlantic sixgill shark)
Notorynchus Ayres, 1855
Notorynchus cepedianus (Péron, 1807) (broadnose sevengill shark)
Extinct species
Family Chlamydoselachidae
Chlamydoselachus Garman, 1884
Chlamydoselachus bracheri Pfeil, 1983
Chlamydoselachus fiedleri Pfeil, 1983
Chlamydoselachus garmani Welton, 1983
Chlamydoselachus goliath Antunes & Cappetta, 2002
Chlamydoselachus gracilis Antunes & Cappetta, 2002
Chlamydoselachus keyesi Mannering & Hiller, 2008
Chlamydoselachus landinii Carrillo-Briceño, Aguilera & Rodriguez, 2014
Chlamydoselachus lawleyi Davis, 1887
Chlamydoselachus tatere Consoli, 2008
Chlamydoselachus thomsoni Richter & Ward, 1990
Chlamydoselachus tobleri Leriche, 1929
Family Crassodontidanidae
Crassodontidanus Kriwet & Klug, 2011
Crassodontidanus serratus Fraas, 1855
Crassodontidanus wiedenrothi Thies, 1983
Notidanoides Maisey, 1986
Notidanoides muensteri Agassiz, 1843
Notidanus Cuvier, 1816
Notidanus amalthei Oppel, 1854
Notidanus atrox Ameghino, 1899
Notidanus intermedius Wagner, 1862
Notidanus nikitini Chabakov & Zonov, 1935
Pachyhexanchus Cappetta, 1990
Pachyhexanchus pockrandti Ward & Thies, 1987
Family Hexanchidae
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 ezoensis Applegate & Uyeno, 1968
Heptranchias howellii Reed, 1946
Heptranchias karagalensis Kozlov in Zhelezko & Kozlov, 1999
Heptranchias tenuidens Leriche, 1938
Hexanchus Rafinesque, 1810
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 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
Family Mcmurdodontidae ?
Mcmurdodus White, 1968
Mcmurdodus featherensis White, 1968
Mcmurdodus whitei Turner, & Young, 1987
Family Orthacodontidae
Occitanodus Guinot, Cappetta & Adnet, 2014
Occitanodus sudrei Guinot, Cappetta & Adnet, 2014
Orthacodus Woodward, 1889
Orthacodus longidens Agassiz, 1843
Sphenodus Agassiz, 1843
Sphenodus alpinus Gümbel, 1861
Sphenodus longidens Agassiz, 1843
Sphenodus lundgreni Davis, 1890
Sphenodus macer Quenstedt, 1852
Sphenodus nitidus Wagner, 1862
Sphenodus planus Agassiz, 1843
Sphenodus rectidens Emmons, 1858
Sphenodus robustidens Seguenza, 1900
Sphenodus tithonius Gemmellaro, 1871
Sphenodus virgai Gemmellaro, 1871
Species
See also
Time range of Hexanchiformes species
Footnotes
References
External links
(Fish Base family reference)
(Fish Base family reference)
Extant Middle Jurassic first appearances
Cartilaginous fish orders
Taxa named by Fernando de Buen y Lozano