Sharks Wallpaper, #10239

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 gill slits. Sharks have a covering of dermal denticles that protect their skin from damage and parasites and improve fluid dynamics; they also have replaceable teeth. 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, freshwater and in deltas.The general rule is that there is only one layer of tesserae in Sharks, but the jaws of large specimens, such as the bull Shark, tiger Shark, and the great white Shark, have been found to be covered with both two and three layers, and even more, depending on the body size. The jaws of a large white Shark even had five layers.Because of this, most Sharks need to constantly swim in order to breathe and can't sleep very long, if at all, or they will sink. However certain Shark species, like the nurse Shark, have spiracles that force water across their gills allowing them for stationary rest on the ocean bottom.