Description
Sharks, squales or selachimorphs are a super-order of cartilagino fish, with five to seven gill slits on the sides of the head and pectoral fins that are not fused to the head. They are found in all the world’s oceans and in some large rivers. Modern sharks are classified in the Selachimorpha or Selachii clade and are the sister group to rays. However, the term "shark", in a broad sense, also refers to extinct species of the subclass Elasmobranchii, such as Cladoselache and Xenacanthus.