Physical Characteristics of Sharks
Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a streamlined body. They respire with the use of five to seven gilldermal denticles that protect their skin from damage and parasites and improve fluid dynamics; they also have replaceable teeth. Shark teeth are prized by collectors for their beauty, and although greatly feared most shark populations have fallen by 90%. Sharks range in size from the small pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 in) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (39 ft) and which, like baleen whales, feeds only on plankton, squid, and small fish through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water and in deltas.
The physical characteristics of sharks are different from those of bony fish, but a large number of species and the diversity of shark habitats mean that there are many variations on the “typical” shark body.