Difference between revisions of "Shark"
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| − | Sharks (suborder | + | Sharks (suborder Selachimorpha) are fish with a cartilaginous skeleton and a an aerodynamic body, partially from a covering of dermal denticles that improve their fluid dynamics as well as protect their skin from damage and parasites. They respire with the use of five to seven gill slits.<ref>Budker, Paul (1971). The Life of Sharks. London: Weidenfeld and Nicolson. SBN 297003070. </ref> They have replaceable teeth. They are some of the world's most misunderstood predators, as they very rarely attack humans unless intimidated. |
Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.<ref>Allen, Thomas B. (1999). The Shark Almanac. New York: The Lyons Press. ISBN 1-55821-582-4.</ref> | Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.<ref>Allen, Thomas B. (1999). The Shark Almanac. New York: The Lyons Press. ISBN 1-55821-582-4.</ref> | ||
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== Characteristics == | == Characteristics == | ||
| − | + | Some sharks have a respiratory systems where their gills do not provide enough oxygen in normal stationary circumstances. Many sharks are afflicted with the inability to stop moving, so to get enough oxygen they must swim continuously. This is known as ram ventilation. | |
| − | Unlike fish, Sharks use oil for bouancy, not gas. This is not as effective as gas, so Sharks are forced to use | + | Unlike fish, Sharks use oil in their liver for bouancy, not gas in a swim bladder. This is not as effective as gas, so Sharks are forced to use dynamic lift while swimming to sink or rise. |
Also unlike fish, Sharks do not drink sea water, but absorb it, meaning they cannot survive in fresh water. | Also unlike fish, Sharks do not drink sea water, but absorb it, meaning they cannot survive in fresh water. | ||
| − | Sharks | + | Sharks, have multiple sets of teeth. Some sharks lose over 30,000 teeth in a lifetime. |
| − | + | Some larger species of sharks such as the Great White are slightly Homeothermic. In mammals, internal body heat is generated, maintained, and regulated by metabolic activity. However in these shark species, they are able to keep their internal body temperature above the ambient water temperature by the presence of the rete mirabile, a counter current exchange mechanism that reduces the loss of body heat and they are also able to generate a small amount of heat through muscular contraction. | |
== Reproduction == | == Reproduction == | ||
| − | + | Unlike most fish, which reproduce by laying large numbers of eggs, sharks usually produce a dozen pups, which are either protected by an egg case or born live. | |
==Classification== | ==Classification== | ||
| − | + | Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks. | |
==References== | ==References== | ||
<references/> | <references/> | ||
Revision as of 01:34, March 17, 2007
Sharks (suborder Selachimorpha) are fish with a cartilaginous skeleton and a an aerodynamic body, partially from a covering of dermal denticles that improve their fluid dynamics as well as protect their skin from damage and parasites. They respire with the use of five to seven gill slits.[1] They have replaceable teeth. They are some of the world's most misunderstood predators, as they very rarely attack humans unless intimidated.
Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.[2]
Characteristics
Some sharks have a respiratory systems where their gills do not provide enough oxygen in normal stationary circumstances. Many sharks are afflicted with the inability to stop moving, so to get enough oxygen they must swim continuously. This is known as ram ventilation.
Unlike fish, Sharks use oil in their liver for bouancy, not gas in a swim bladder. This is not as effective as gas, so Sharks are forced to use dynamic lift while swimming to sink or rise.
Also unlike fish, Sharks do not drink sea water, but absorb it, meaning they cannot survive in fresh water.
Sharks, have multiple sets of teeth. Some sharks lose over 30,000 teeth in a lifetime.
Some larger species of sharks such as the Great White are slightly Homeothermic. In mammals, internal body heat is generated, maintained, and regulated by metabolic activity. However in these shark species, they are able to keep their internal body temperature above the ambient water temperature by the presence of the rete mirabile, a counter current exchange mechanism that reduces the loss of body heat and they are also able to generate a small amount of heat through muscular contraction.
Reproduction
Unlike most fish, which reproduce by laying large numbers of eggs, sharks usually produce a dozen pups, which are either protected by an egg case or born live.
Classification
Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks.