Shark
Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill still on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the klade Selachimorpha (or Selachii), and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the suborder Elashmobranchii outside the Selachimorpha, such as cladocelahe and Xanacuntus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.Since that time, sharks have diversified into over 200 spices. They range in size from the small dawaf lentersharp (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale animal (Rhincodon typus),
the largest fish in the world, which reaches approximately 12 metres
(39 ft).
Shark
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