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Hexanchiformes

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Title: Hexanchiformes  
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Subject: Chondrichthyes, Shark, Bigeyed sixgill shark, Bluntnose sixgill shark, Frilled shark
Collection: Hexanchiformes, Middle Jurassic First Appearances
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Hexanchiformes

Hexanchiformes
Temporal range: Middle Jurassic–Recent
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[1]
Frilled shark, Chlamydoselachus anguineus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Selachimorpha
Order: Hexanchiformes
F. de Buen, 1926
Families

Crassonotidae
Mcmurdodontidae
Orthacodontidae
Chlamydoselachidae
Hexanchidae

Hexanchiformes is the order consisting of the most primitive types of sharks, and numbering just six extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.[2]

Hexanchiform sharks have only one dorsal fin, either six or seven gill slits, and no nictitating membrane in the eyes.

The frilled shark, Chlamydoselachus anguineus, is very different from the cow sharks, and it has been proposed that it be moved to its own order, Chlamydoselachiformes.

Contents

  • Classification 1
    • Living species 1.1
    • Extinct species 1.2
  • Species 2
  • See also 3
  • References 4

Classification

Living species

Extinct species

Notidanodon sp. fossil at the Geological Museum, Copenhagen

Species

Family Image Common name Genera Species Description
Chlamydoselachidae Frilled sharks 1
extant
1
extinct
2
extant
12
extinct
Frilled sharks contain only two extant species of deep sea creatures who are typically weakened in areas closer to the surface. The most widely known species still surviving is the frilled shark, known as a living fossil, along with the Southern African frilled shark, found along coastal areas of South Africa. There are several extinct species.
†Crassonotidae Crassonotidae 4 8 Extinct.
Hexanchidae Cow sharks 3
extant
5
extinct
4
extant
31
extinct
Cow sharks are considered the most primitive of all the sharks, because their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialised, suggesting that 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 addition to the five found in all other sharks.[3] They range from 1.4 metres (4.6 ft) to over 5.5 metres (18 ft) in adult body length.
†Mcmurdodontidae Mcmurdodontidae 1 2 Extinct.
†Orthacodontidae Orthacodontidae 3 12 Extinct.

See also

References

  1. ^ Froese, Rainer, and Daniel Pauly, eds. (2009). "Hexanchiformes" in FishBase. January 2009 version.
  2. ^ Allen, 45
  3. ^ Matt's, J. & Last P.R. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. p. 61.  
  • Froese, Rainer, and Daniel Pauly, eds. (2011). "Chlamydoselachidae" in FishBase. February 2011 version. (Fish Base family reference)
  • Froese, Rainer, and Daniel Pauly, eds. (2011). "Hexanchidae" in FishBase. February 2011 version. (Fish Base family reference)
  • Allen, Thomas B. (1999). The Shark Almanac. New York: The Lyons Press.  
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