Euselachii

Euselachii are an infraclass of a class of cartilaginous fish. This group includes sharks and rays.[2][3][4]

Oceanic Whitetip Shark

Euselachii
Temporal range:
Silurian-Holocene[1]
Tiger Shark
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Infraclass: Euselachii
Hay, 1902
Orders

See text

Taxonomy
White shark

Of the 14 orders that compose Euselachii, 8 belong to the sharks, 6 to the rays, without an intermediate taxon separating sharks of rays. For this reason, some authors have separated Euselachii in two:

super-order Selachimorpha corresponding to orders of sharks; super-order Rajomorphii corresponding to the orders of rays, torpedoes, sawfish and guitar fish. For those who do not recognize these two super-orders, Euselachii therefore has for synonyms Pleurotremata, Selachimorpha and Rajomorphii.

Reproduction

Both oviparity and viviparity are found in Euselachii. Around 70% of sharks are viviparous[5], including some members of Carcharhiniformes such as requiem sharks and hammerhead sharks, while the remaining 30% of sharks as well as all rays are either oviparous or ovoviviparous.

Squatina squatina

Physical Appearance

There was a recent discovery that a Palaeozoic chondrichthyan (carcharopsis) was found to no longer resemble the "triple-layer" tooth structure that the modern day chondrichthyan sharks model.

List of Orders
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References
  1. "Infraclass Euselachii Hay 1902". Fossilworks.org.
  2. Nelson, J. S. (2006). Fishes of the World (4 ed.). Hoboken, NJ: John Wiley & Sons. p. 49. ISBN 978-0-471-25031-9.
  3. "Euselachii". Integrated Taxonomic Information System. Retrieved 21 May 2018.
  4. "Fish glossary". FishBase.
  5. "Mating and Reproduction of Sharks", Shark Foundation
  6. J. A. Long. 2011. The Rise of Fishes: 500 Million Years of Evolution (Second Edition) 1-287 [G. Lloyd/G. Lloyd/M. Uhen]
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