Kingdom: Animalia

Phylum: Chordata

Class: Chondrichthyes

Subclass: Elasmobranchii

Infraclass: Euselachii

Superorder: Selachimorpha

Order: Hexanchiformes


The order Hexanchiformes contains two families. The Frilled sharks, or Chlamydoselachidae, and the Cow sharks, or Hexanchidae.

These sharks can be found all over the world in tropical, temperate and boreal waters. They prefer deep, cold habitats mostly in the tropics. However, they can be found inshore in temperate temperatures as well.

Hexanchiformes typically have 6 or 7 gill slits. Their vertebral column extends all the way to the caudal fin’s long dorsal lobe. They have one spineless dorsal fin over or behind the pelvic fins. There is an anal fin present.

They have large mouths, and eyes positioned on the side of the head, with small spiracles above and behind the eyes. They do not have nictitating membranes.

The Frilled and Cow sharks are very different, and some scientists have proposed to separate the two into their own unique orders. However, this hasn’t been accepted.

Most of the families and species belonging to the order Hexanchiformes are quite primitive, and extinct. Most fossils of extinct species are traced back from Jurassic, Devonian and Permian periods. Shark teeth similar to those 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 after the Permian extinction (and by extension, the oldest extant order of elasmobranchs) Below is a list of both living and extinct families. Visit our Primitive Sharks’ section in the Planet Shark Diver’s Academy to learn more of some of these families and species.

Living Families:

Chlamydoselachidae: Frilled Sharks

Hexanchidae: Cow Sharks


Extinct Families:


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

Proteothrinax Pfeil, 1983

Proteothrinax baumgartneri Pfeil, 1983


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


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

Mcmurdodontidae ?

Mcmurdodus White, 1968

Mcmurdodus featherensis White, 1968

Mcmurdodus whitei Turner, & Young, 1987


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