Euselachii


Euselachii are an infraclass of a class of cartilaginous fish. This group includes sharks and rays.

Taxonomy

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, 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.

Physical Appearance

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

List of Orders