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Shark

Shark

Hexanchiformes
Squaliformes
Pristiophoriformes
Squatiniformes
Heterodontiformes
Orectolobiformes
Carcharhiniformes
Lamniformes Sharks are a group (superorder Selachimorpha) of fish, with a full cartilaginous skeleton, a streamlined body plan, with normally 5, but up to 7 (depending on species) gill slits along the side of, or beginning slightly behind, the head (in some species, a modified slit called a spiracle, is located just behind the eye), dermal denticles covering the body to protect from damage, parasites and improve fluid dynamics, and rows of replaceable teeth in the mouth.

Characteristics

mouth]Sharks have keen olfactory senses, with some species able to detect as little as one part per million of blood in seawater. They are even more attracted to the chemicals found in the gut of many species, and often linger near or in sewage outfalls. Some species, such as Nurse Sharks, have external barbels that greatly increase their ability to sense prey. Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to their marine environment with the help of a tissue called, tapetum lucidum. This tissue is behind the retina and reflects light back to the retina, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have nictitating membranes. This membrane covers the eyes during predation, and when it is being attacked. Sharks generally rely on their superior sense of smell to find prey, but once they are close they also use the lateral lines running along their sides to sense movement in the water and also employ special sensory pores on their heads (Ampullae of Lorenzini) to detect electrical pulses created by the muscles of prey. Their teeth are not attached to the jaw, but embedded in their flesh, and in many species are constantly replaced throughout the shark's life. The lower teeth are primarily used for holding prey, while the top are used for cutting into it. (Gilbertson, 7.3) prey There are exceptions to the "large", "marine" (as in 'ocean-going') and "predatory" portions of the characterization. Sharks include everything from the hand-sized Pygmy Shark, a deep sea species, to the Whale Shark, the largest fish (although sharks are not closely related to bony fish) which is known to grow to a maximum length of approximately 15m (49 feet) and which, like the great whales, feeds only on plankton. Although not unique among sharks, the Bull Shark is the better known of several species to regularly swim in both salt and fresh water environments (most famously in Lake Nicaragua, in Central America). A few of the larger species, the Mako and White Shark, are mildly homeothermic, able to maintain their body temperature at a level above the ocean's temperature. This is possible because of the presence of the rete mirabile, a counter current exchange mechanism that reduces the loss of body heat. Like other fish, sharks extract their oxygen from seawater as it passes over their gills. Due to their size and the nature of their metabolism, sharks have a higher demand for oxygen than most fish and they cannot rely on ambient water current to provide an adequate supply of oxygenated water. If a shark were to stop swimming, the necessary water circulation for respiration would become too low and the animal could suffocate. Some sharks, like the Blacktip Reef Shark and Nurse Shark, can pump water over their gills as they rest. There are also known instances, such as in certain caves along the Yucatan coast, where sharks of varying species rest on the cave floors and allow the fresh water outflow to pass over them. The outflow is strong enough to allow for respiration, and it is believed that the reason for this behaviour is that the fresh water helps remove certain parasites. Also, unlike other fish, sharks do not have gas-filled swim bladders, but rather rely on an oil-filled liver for (limited) buoyancy, so they sink when they stop swimming; a resting shark always sinks to the sea bed. A shark, if inverted, enters a natural state of paralysf time. Researchers use this condition for handling sharks safely. A popular myth is that sharks are immune to disease and cancer, however, this is untrue and there are both diseases and parasites that affect sharks. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that have shown sharks to have heightened immunity to disease. [http://news.nationalgeographic.com/news/2003/08/0820_030820_sharkcancer.html]

Shark Attacks

The fear of sharks has been fueled worldwide by a few unusual instances of unprovoked attack, such as the Jersey Shore Shark Attacks of 1916, and by sensationalized fiction and film, such as the Jaws series. While sharks cause a few dozen human deaths annually, it is relatively not a large number (e.g. several hundred people die anually struck by lightning; however, lightning may strike anywhere worldwide, whereas only a very small part of human population is susceptible to shark attacks, i.e. only those people who enter the water in the areas populated by sharks). Contrary to popular belief, only a few sharks are dangerous to humans. Out of the more than 360 described species of sharks, only 4 have been confirmed to have killed humans: the Great White, Tiger, Bull, and Oceanic Whitetip sharks. These sharks, being large, powerful predators perfectly capable of eating humans, will sometimes attack and kill people, but all of the above sharks, even the Great White, have been filmed in open water, with no cage, time and time again, without incident. There are many theories about why sharks attack people. Some claim that the shark is confusing a human for a seal or other prey animal; this would be typical in the case of an attack against a surfer. Often the shark that attacks a human will make only one bite and then go away. This behaviour has many possible explanations, one being that humans don't taste good (or at least, as good), or are lacking the necessary fat, and another being that sharks normally make one swift attack, and then retreat and wait for the victim to die, or exhaust itself, before it comes back to feed. This protects the shark from retribution from a wounded and aggressive target, but also allows humans the time to get out of the water and survive. A number of other species (perhaps 10 - 15) have threatened, attacked, and/or bitten (but not killed) humans without being obviously provoked. This group contains the Mako, Hammerhead, Gray Reef, Black Tip Reef, Lemon, Silky and Blue sharks. These sharks are also large, powerful predators which can be provoked simply by being in the water at the wrong time and place, but they are normally considered less dangerous to divers and swimmers than the previous group. In most cases, if a person moves away calmly, or remains still, they will be ignored. Many shark species are known to "display" when feeling threatened, and it is ill-advised to remain in the vicinity at such a time as this would generally be considered enough provocation to warrant an attack. A few other shark species do attack people every year, producing wounds that can potentially kill, but this occurs either specifically because they have been provoked, or through mistaken identity due to water conditions or the like.

Speed

In general, sharks swim ("cruise") at an average speed of five miles (8.25 kilometers) per hour, but when feeding or attacking, the average shark will reach speeds upwards of twelve miles (19.25 kilometers) per hour. One exception to this generality is the Mako shark, whose speed may range upwards of thirty miles (48 kilometers) per hour. The Mako shark is generally considered to be the fastest species of shark, and may be the fastest of all fish (for short bursts). Another exception, the Great White, the largest actively predatory shark, is capable of surprising bursts of speed. These exceptions may be due to the "warm-blooded", or homeothermic, nature of their physiology.

Etymology

Until the late 16th century sharks were usually referred to in the English language as sea-dogs. The name "Shark" first came into use around the late 1560s to refer to the large sharks of the Caribbean Sea, and later to all sharks in general. The name may have been derived from the Mayan word for shark, xoc, pronounced "shock" or "shawk". The collective noun for a group of sharks is a shiver.

Classification

shiver 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. There are more than 360 described species of sharks. The first sharks appeared in the oceans 400 to 350 million years ago. Most of the species we know today are as old as the Jurassic period. There are eight orders of sharks, listed below in roughly their evolutionary relationship from more primitive to more modern species:
- Hexanchiformes: Examples from this group include the cow sharks, frilled shark and even a shark that looks on first inspection to be a marine snake.
- Squaliformes: Examples from this group include the bramble sharks, dogfish sharks and roughsharks.
- Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing the fishes that they subsequently eat.
- Squatiniformes: Angel sharks.
- Heterodontiformes: They are commonly referred to as the bullhead or horn sharks.
- Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs and the largest of all fishes, the whale shark.
- Carcharhiniformes: They are commonly referred to as the groundsharks, and some of the species include the blue, tiger, bull, reef and oceanic whitetip sharks (collectively called the requiem sharks) along with the houndsharks, catsharks and hammerhead sharks. They are distinguished by an elongated snout and a nictitating membrane which protects the eyes during an attack.
- Lamniformes: They are commonly referred to as the mackerel sharks. They include the goblin shark, basking shark, megamouth shark, the thresher sharks, mako shark and great white shark. They are distinguished by their large jaws and ovoviviparous reproduction. The Lamniformes include the extinct Megalodon (Carcharodon megalodon), which like all extinct sharks is only known from its teeth (the only bone found in these cartilaginous fishes, and therefore the only fossils produced). A reproduction of the jaw was based on some of the largest teeth (up to almost 17 cm (7 inches) in length) and suggested a fish that could grow 15 m (50 feet) long. The jaw was realized to be inaccurate, and estimates revised downwards to around 6 m (20 feet).

Reproduction

The sex of a shark can be easily determined. The males all have their pelvic fins modified into a pair of claspers. The name is somewhat misleading as they are not used to hold on to the female, but are the shark's version of the mammalian penis. (As a side note, Class Chondrichthyes has the distinction of having the animal with the largest intromittent organ — an organ used for transmitting sperm — in relation to body length. This animal is the clearnose skate (Raja eglanteria) which has claspers of 15 cm (6 in) in size on a fish that reaches 1 m (3 feet) in length.) Mating has rarely been observed in sharks. The smaller catsharks often mate with the male curling around the female. In the less flexible species the two sharks swim parallel to each other while the male inserts the clasper into the female's oviduct. Many females in the larger species have bite marks that appear to be a result of a male grasping her to maintain position. The bite marks can also come from the courtship of the sharks. The male may come and bite the edges of the female to show his interest. In some species, females have evolved thicker skin to withstand the sharks bite marks during mating. Sharks have a much different reproductive strategy than most fishes. Instead of producing huge numbers of eggs and larvae (99.9% of which never reach sexual maturity in fishes that use this strategy) sharks normally produce around a dozen pups, some species up to 70-80 and some as few as 2-3. These pups are either protected by egg cases or born live. No known sharks provide parental protection for their young, but females have a hormone that is released into their blood during the pupping season that apparently keeps them from feeding. hormone]] There are three ways in which shark pups are born:
- Oviparity - Some sharks lay eggs. In most of these species, the developing embryo is protected by an egg case with the consistency of leather. Some of these cases are corkscrewed into crevices for protection. When they wash up empty on beaches, the egg cases are sometimes called mermaid's purses. Oviparous sharks include the horn shark, catsharks, Port Jackson Sharks, and the swell shark.
- Viviparity - These sharks actually maintain a placental link to the developing young, more analogous to mammals than other fishes. The young are born alive and fully functional. Hammerheads, the requiem sharks (like the bull and tiger sharks), the basking shark and the smooth dogfishes fall into this category. Dogfishes also have the longest known gestation period of any shark, 22 months. The blue shark produces the most young of sharks that have had the number of pups recorded, the maximum reported being 82.
- Ovoviviparity - Most sharks utilize this method. The young are nourished by the yolk of their egg and by fluids secreted by glands in the walls of the oviduct. The eggs hatch within the oviduct, and the young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. Sometimes they are functional even before being born, as some species practice oophagy, where the first to hatch eat the remaining eggs in the oviduct. Sand tigers, makos, threshers, porbeagles and possibly great whites have oophagous young. The survival strategy for the species that do this is that the young are able to grow to an even larger size before being born. The whale shark is now considered to be in this category after having been classified as oviparous for a long time. Whale shark eggs found are now thought to have been aborted. Most ovoviviparous sharks generally give birth in sheltered areas, including bays, river mouths, and shallow reefs. They choose such areas mainly because of the protection from predators (mainly other sharks) and the abundance of food.

Shark senses

Sharks have two senses that many animals do not have:
- Electroreception: The Ampullae of Lorenzini are small pits in the head that detect electricity. The shark has the greatest electricity sensitivity known in all animals. This sense is used to find prey hidden in sand in bottom feeding sharks, by detecting the nerve impulses. It is this sense that sometimes confuses a shark into attacking a boat, when the metal interacts with the salt water. They can track these things from the top around a mile away, and it not only senses prey, it can sense other things as well! It is almost like having a small camera in the shark's eye, but not really. It can sense that if there is a prey, or if it is a predator, or if it is just a spectator watching it.
- Lateral line - This system is found in most fishes, including sharks. It is used to detect motion or 'sound' in the water. The shark uses this to detect other organisms moving, especially wounded fish. The shark can 'hear' frequencies in the range of 25 to 50 Hz using this sense. Lateral line

Shark fishery

Each year, 100 million sharks are killed by people in commercial and recreational fishing. In the past they were fished simply for the sport of landing a good fighting fish (mako sharks for instance). Sharkskin (covered in effect with tiny teeth - dermal denticles) was used for the purposes that sandpaper currently is, others for food (Atlantic thresher, mako and others), and some species for other products. Sharks are a common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria Shark is the most commonly used fish in fish and chips, in which fillets are battered and deep fried or crumbed and grilled and served alongside chips. When served in fish and chip shops, it is called Flake. Sharks are often killed for shark fin soup, in which many sharks are hunted for their fins, which are cut off with a hot metal blade before the live animal is tossed back into the water. There have been cases where hundreds of de-finned animals were swept up on local beaches without any way to convey themselves back into the sea. Conservationists have campaigned for changes in the law to make finning illegal in the U.S. Sharks generally reach sexual maturity slowly and produce very few offspring in comparison to other fishes that are harvested. This has caused concern among biologists regarding the increase in effort applied to catching sharks over time, and many species are considered to be threatened. Organizations like the Shark Trust are trying to limit shark fishing.

Sharks in mythology

Sharks figure prominently in the Hawaiian mythology. There are stories of shark men who have shark jaws on their back. They could change form between shark and human at any time desired, and for any length. A common theme in the stories was that the shark men would warn beach goers that sharks were in the waters. The beach goers would laugh and ignore the warnings and go swimming, subsequently being eaten by the same shark man who warned them not to enter the water. Hawaiian mythology also contained many shark gods. They believed that sharks were guardians of the sea, and called them Aumakua. A listing of them follows:

- Kamohoali'i - The most well known and revered of the shark gods, he was the older and favored brother of Pele, and helped and journeyed with her to Hawaii. He was able to take on all human and fish forms. A summit cliff on the crater of Kilauea is considered to be one of his most sacred spots. At one point he had a he'iau (temple or shrine) dedicated to him on every piece of land that jutted into the ocean on the island of Moloka'i.
- Ka'ahupahau - This goddess was born human, with her defining characteristic being her red hair. She was later transformed into shark form and was believed to protect the people who lived on O'ahu from sharks. She was also believed to live near Pearl Harbor.
- Kaholia Kane - This was the shark god of the ali'i Kalaniopu'u and he was believed to live in a cave at Puhi, Kaua'i.
- Kane'apua - Most commonly, he was the brother of Pele and Kamohoali'i. He was a trickster god who performed many heroic feats, including the calming of two legendary colliding hills that destroyed canoes trying to pass between.
- Kawelomahamahai'a - Another human, he was transformed into a shark.
- Keali'ikau 'o Ka'u - He was the cousin of Pele and son of Kua. He was called the protector of the Ka'u people. He had an affair with a human girl, who gave birth to a helpful green shark.
- Kua - This was the main shark god of the people of Ka'u, and believed to be their ancestor.
- Kuhaimoana - He was the brother of Pele and lived in the Ka'ula islet. He was said to be 30 fathoms (55 m) long and was the husband of Ka'ahupahau.
- Kauhuhu - He was a fierce king shark that lived in a cave in Kipahulu on the island of Maui. He sometimes moved to another cave on the windward side of island of Moloka'i.
- Kane-i-kokala - A kind shark god that saved shipwrecked people by taking them to shore. The people who worshipped him feared to eat, touch or cross the smoke of the kokala, his sacred fish. The Basking shark is a shark that will never eat a human. The black tip diving shark will can dive up to 250 feet down. In other Pacific Ocean cultures, Dakuwanga was a shark god who was the eater of lost souls. In ancient Greece, shark flesh was forbidden to be eaten at women's festivals.

Sharks in popular culture

References

- Gilbertson, Lance (1999). Zoology Laboratory Manual. New York, McGraw-Hill Companies, Inc.
- Castro, Jose. The Sharks of North American Waters. College Station: Texas A&M University Press, 1983.
- Stevens, John D. Sharks. New York: NY Facts on File Publications, 1987.

External links

- [http://www.geerg.ca Greenland Shark and Elasmobranch Education and Research Group]
- [http://www.flmnh.ufl.edu/fish/Sharks/ISAF/ISAF.htm The International Shark Attack File]
- [http://www.sharktrust.org/sharkconservation.html Shark Trust Organization]
- [http://www.elasmo-research.org ReefQuest Centre for Shark Research]
- [http://www.jostimages.com/galerie/sharks/index.html Photographs of sharks]
- [http://www.robertosozzani.it/Sharks/cont.html Sharks Photo gallery]
- [http://www.sharkology.com Sharkology]
- [http://www.onewhale.com/sharks.htm Shark cartoons] ko:상어 ja:サメ

Hexanchiformes

Chlamydoselachidae (frilled shark)
Hexanchidae (cow sharks) Hexanchiformes is the order consisting of the most primitive types of sharks, and numbering just five extant species. Hexanchiform sharks have only one dorsal fin, either six or seven gill slits, and no nictitating membrane in the eyes. The frilled shark, Chlamydoselachus anguineus, is very different from the cow sharks, and it has been proposed that it be moved to its own order Chlamydoselachiformes.

Classification

Extant species

Family Chlamydoselachidae
- Chlamydoselachus
- Chlamydoselachus anguineus Garman, 1884 (Frilled shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=635&genusname=Chlamydoselachus&speciesname=anguineus] Family Hexanchidae
- Heptranchias
- Heptranchias perlo (Bonnaterre, 1788) (Sharpnose sevengill shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=636&genusname=Heptranchias&speciesname=perlo]
- Hexanchus
- Hexanchus griseus (Bonnaterre, 1788) (Bluntnose sixgill shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=637&genusname=Hexanchus&speciesname=griseus]
- Hexanchus nakamurai Teng, 1962 (Bigeye sixgill shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=638&genusname=Hexanchus&speciesname=nakamurai]
- Notorynchus
- Notorynchus cepedianus (Péron, 1807) (Broadnose sevengill shark or spotted sevengill shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=2531&genusname=Notorynchus&speciesname=cepedianus]

Extinct species

Family Chlamydoselachidae
- Chlamydoselachus
- Chlamydoselachus bracheri Pfeil, 1983
- Chlamydoselachus gracilis Antunes & Cappetta, 2001
- Chlamydoselachus goliath Antunes & Cappetta, 2001
- Chlamydoselachus fiedleri Pfeil, 1983
- Chlamydoselachus lawleyi Davis, 1887
- Chlamydoselachus thomsoni Richter & Ward, 1990
- Chlamydoselachus tobleri Leriche, 1929
- Thrinax
- Thrinax baumgartneri Pfeil, 1983 Family Heptranchidae
- Heptranchias
- Heptranchias ezoensis Applegate & Uyeno, 1968
- Heptranchias howelii (Reed, 1946)
- Heptranchias perlo (Bonnaterre, 1788)[http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=636&genusname=Heptranchias&speciesname=perlo]
- Heptranchias tenuidens (Leriche, 1938) Family Hexanchidae
- Hexanchus
- Hexanchus arzoensis (Debeaumont, 1960)
- Hexanchus agassizi [http://www.sheppeyfossils.com/pages/hexanchus_agassizi.htm]
- Hexanchus collinsonae Ward, 1979
- Hexanchus gracilis (Davis, 1887)
- Hexanchus griseus (Bonaterre, 1788) [http://home.tiscali.be/belgiansharkteeth/post_oligocene/sharks/hexachus.htm]
- Hexanchus griseus “andersoni” “gigas” (Bonaterre, 1788)
- Hexanchus hookeri Ward, 1979
- Hexanchus microdon “agassizii” (Agassiz, 1843)
- Hexanchus nakamurai “vitulus” Teng, 1962
- Notidanoides
- Notidanodon
- Notidanodon antarcti Grande & Chatterjee, 1987
- Notidanodon brotzeni Siverson, 1995
- Notidanodon dentatus (Woodward, 1886)
- Notidanodon lanceolatus (Woodward, 1886)
- Notidanodon loozi (Vincent, 1876)
- Notidanodon pectinatus (Agassiz, 1843)
- Notorynchus
- Notorynchus aptiensis (Pictet, 1865)
- Notorynchus intermedius Wagner
- Notorynchus lawleyi Ciola & Fulgosi, 1983
- Notorynchus munsteri (Agassiz, 1843)
- Notorynchus cepedianus (Peron, 1807)
- Notorynchus serratissimus (Agassiz, 1844)
- Notorynchus serratus (Agassiz, 1844)
- Paraheptranchias
- Paraheptranchias repens (Probst, 1879)
- Paranotidanus “Eonotidanus” contrarius (Munster, 1843)
- Paranotidanus intermedius (Wagner, 1861)
- Paranotidanus munsteri (Agassiz, 1843)
- Paranotidanus serratus (Fraas, 1855)
- Pseudonotidanus
- Pseudonotidanus semirugosus Underwood & Ward, 2004
- Weltonia
- Weltonia ancistrodon (Arambourg, 1952)
- Weltonia burnhamensis Ward, 1979 Family ?Mcmurdodontidae
- Mcmurdodus
- Mcmurdodus featherensis White, 1968
- Mcmurdodus whitei Turner, & Young, 1987

Squaliformes

Squalidae (dogfish sharks)
Centrophoridae (gulper sharks)
Dalatiidae (sleeper sharks)
Echinorhinidae (bramble sharks) Squaliformes is an order of sharks that includes the smooth dogfish and spiny dogfish and others, about 80 species in four families. Members of the order have two dorsal fins, no anal fin, and no nictitating membrane. They have five gill slits.

Classification

Family Echinorhinidae
- Echinorhinus
- Echinorhinus brucus (Bonnaterre, 1788) (Bramble shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=641&genusname=Echinorhinus&speciesname=brucus]
- Echinorhinus cookei Pietschmann, 1928 (Prickly shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=642&genusname=Echinorhinus&speciesname=cookei] Family Centrophoridae
- Centrophorus
- Centrophorus acus Garman, 1906 (Needle dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=647&genusname=Centrophorus&speciesname=acus]
- Centrophorus granulosus (Bloch & Schneider, 1801) (Gulper Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=648&genusname=Centrophorus&speciesname=granulosus]
- Centrophorus harrissoni McCulloch, 1915 (Dumb gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=649&genusname=Centrophorus&speciesname=harrissoni]
- Centrophorus lusitanicus Barbosa du Bocage & Brito Capello, 1864 (Lowfin gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=650&genusname=Centrophorus&speciesname=lusitanicus]
- Centrophorus moluccensis Bleeker, 1860 (Smallfin gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=651&genusname=Centrophorus&speciesname=moluccensis]
- Centrophorus niaukang Teng, 1959 (Taiwan gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=652&genusname=Centrophorus&speciesname=niaukang]
- Centrophorus squamosus (Bonnaterre, 1788) (Leafscale gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=653&genusname=Centrophorus&speciesname=squamosus]
- Centrophorus tesselatus Garman, 1906 (Mosaic gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=654&genusname=Centrophorus&speciesname=tessellatus]
- Centrophorus uyato (Rafinesque, 1810) (Little gulper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=655&genusname=Centrophorus&speciesname=uyato]
- Deania
- Deania calcea (Lowe, 1839) (Birdbeak dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=670&genusname=Deania&speciesname=calcea]
- Deania hystricosa (Garman, 1906) (Rough longnose dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=671&genusname=Deania&speciesname=hystricosa]
- Deania profundorum (Smith & Radcliffe, 1912) (Arrowhead dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=672&genusname=Deania&speciesname=profundorum]
- Deania quadrispinosum (McCulloch, 1915) (Longsnout dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=673&genusname=Deania&speciesname=quadrispinosum] Family Dalatiidae
- Aculeola
- Aculeola nigra de Buen, 1959 (Hooktooth dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=644&genusname=Aculeola&speciesname=nigra]
- Centroscyllium
- Centroscyllium excelsum Shirai & Nakaya, 1990 (Highfin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53965&genusname=Centroscyllium&speciesname=excelsum]
- Centroscyllium fabricii (Reinhardt, 1825) (Black dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=656&genusname=Centroscyllium&speciesname=fabricii]
- Centroscyllium granulatum Günther, 1887 (Granular dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=657&genusname=Centroscyllium&speciesname=granulatum]
- Centroscyllium kamoharai Abe, 1966 (Bareskin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=658&genusname=Centroscyllium&speciesname=kamoharai]
- Centroscyllium nigrum Garman, 1899 (Combtooth dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=660&genusname=Centroscyllium&speciesname=nigrum]
- Centroscyllium ornatum (Alcock, 1889) (Ornate dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=659&genusname=Centroscyllium&speciesname=ornatum]
- Centroscyllium ritteri Jordan & Fowler, 1903 (Whitefin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=661&genusname=Centroscyllium&speciesname=ritteri]
- Centroscymnus
- Centroscymnus coelolepis Barbosa du Bocage & Brito Capello, 1864 (Portuguese dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=662&genusname=Centroscymnus&speciesname=coelolepis]
- Centroscymnus crepidater (Barbosa du Bocage & Brito Capello, 1864) (Longnose velvet dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=663&genusname=Centroscymnus&speciesname=crepidater]
- Centroscymnus cryptacanthus Regan, 1906 (Shortnose velvet dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=664&genusname=Centroscymnus&speciesname=cryptacanthus]
- Centroscymnus macracanthus Regan, 1906 (Largespine velvet dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=665&genusname=Centroscymnus&speciesname=macracanthus]
- Centroscymnus owstoni Garman, 1906 (Roughskin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=666&genusname=Centroscymnus&speciesname=owstoni]
- Centroscymnus plunketi (Waite, 1910) (Plunket shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=667&genusname=Centroscymnus&speciesname=plunketi]
- Cirrhigaleus
- Cirrhigaleus asper (Merrett, 1973) (Roughskin spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=707&genusname=Cirrhigaleus&speciesname=asper]
- Cirrhigaleus barbifer Tanaka, 1912 (Mandarin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=668&genusname=Cirrhigaleus&speciesname=barbifer]
- Dalatias
- Dalatias licha (Bonnaterre, 1788) (Kitefin shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=669&genusname=Dalatias&speciesname=licha]
- Etmopterus
- Etmopterus baxteri Garrick, 1957 (New Zealand lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=54017&genusname=Etmopterus&speciesname=baxteri]
- Etmopterus brachyurus Smith & Radcliffe, 1912 (Shorttail lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=675&genusname=Etmopterus&speciesname=brachyurus]
- Etmopterus bullisi Bigelow & Schroeder, 1957 (Lined lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=676&genusname=Etmopterus&speciesname=bullisi]
- Etmopterus carteri Springer & Burgess, 1985 (Cylindrical lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=50208&genusname=Etmopterus&speciesname=carteri]
- Etmopterus decacuspidatus Chan, 1966 (Combtooth lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=677&genusname=Etmopterus&speciesname=decacuspidatus]
- Etmopterus gracilispinis Krefft, 1968 (Broadband lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=678&genusname=Etmopterus&speciesname=gracilispinis]
- Etmopterus granulosus (Günther, 1880) (Southern lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=679&genusname=Etmopterus&speciesname=granulosus]
- Etmopterus hillianus (Poey, 1861) (Caribbean lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=680&genusname=Etmopterus&speciesname=hillianus]
- Etmopterus lucifer Jordan & Snyder, 1902 (Blackbelly lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=681&genusname=Etmopterus&speciesname=lucifer]
- Etmopterus perryi Springer & Burgess, 1985 (Dwarf lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=50209&genusname=Etmopterus&speciesname=perryi]
- Etmopterus polli Bigelow, Schroeder & Springer, 1953 (African lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=682&genusname=Etmopterus&speciesname=polli]
- Etmopterus princeps Collett, 1904 (Great lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=683&genusname=Etmopterus&speciesname=princeps]
- Etmopterus pusillus (Lowe, 1839) (Smooth lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=684&genusname=Etmopterus&speciesname=pusillus]
- Etmopterus schultzi Bigelow, Schroeder & Springer, 1953 (Fringefin lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=685&genusname=Etmopterus&speciesname=schultzi]
- Etmopterus sentosus Bass, D'Aubrey & Kistnasamy, 1976 (Thorny lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=686&genusname=Etmopterus&speciesname=sentosus]
- Etmopterus spinax (Linnaeus, 1758) (Velvet belly) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=687&genusname=Etmopterus&speciesname=spinax]
- Etmopterus unicolor (Engelhardt, 1912) (Brown lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=688&genusname=Etmopterus&speciesname=unicolor]
- Etmopterus villosus Gilbert, 1905 (Hawaiian lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=689&genusname=Etmopterus&speciesname=villosus]
- Etmopterus virens Bigelow, Schroeder & Springer, 1953 (Green lanternshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=690&genusname=Etmopterus&speciesname=virens]
- Euprotomicroides
- Euprotomicroides zantedeschia Hulley & Penrith, 1966 (Taillight shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=691&genusname=Euprotomicroides&speciesname=zantedeschia]
- Europtomicrus
- Euprotomicrus bispinatus (Quoy & Gaimard, 1824) (Pygmy shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?genusname=Euprotomicrus&speciesname=bispinatus]
- Heteroscymnoides
- Heteroscymnoides marleyi Fowler, 1934 (Longnose pygmy shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=694&genusname=Heteroscymnoides&speciesname=marleyi]
- Isistius
- Isistius brasiliensis (Quoy & Gaimard, 1824) (Cookiecutter shark cigar shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=696&genusname=Isistius&speciesname=brasiliensis]
- Isistius labialis Meng, Zhu & Li, 1985 () [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=61220&genusname=Isistius&speciesname=labialis]
- Isistius plutodus Garrick & Springer, 1964 (Largetooth cookiecutter shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=697&genusname=Isistius&speciesname=plutodus]
- Mollisquama
- Mollisquama parini Dolganov, 1984 (Softskin dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53994&genusname=Mollisquama&speciesname=parini]
- Oxynotus
- Oxynotus bruniensis (Ogilby, 1893) (Prickly dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=715&genusname=Oxynotus&speciesname=bruniensis]
- Oxynotus caribbaeus Cervigón, 1961 (Caribbean roughshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=717&genusname=Oxynotus&speciesname=caribbaeus]
- Oxynotus centrina (Linnaeus, 1758) (Angular roughshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=718&genusname=Oxynotus&speciesname=centrina]
- Oxynotus japonicus Yano & Murofushi, 1985 (Japanese roughshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=54012&genusname=Oxynotus&speciesname=japonicus]
- Oxynotus paradoxus Frade, 1929 (Sailfin roughshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=719&genusname=Oxynotus&speciesname=paradoxus]
- Scymnodalatias
- Scymnodalatias albicauda Taniuchi & Garrick, 1986 (Whitetail dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=27194&genusname=Scymnodalatias&speciesname=albicauda]
- Scymnodalatias garricki Kukuyev & Konovalenko, 1988 (Kukuyev & Konovalenko, 1988) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53990&genusname=Scymnodalatias&speciesname=garricki]
- Scymnodalatias oligodon Kukuyev & Konovalenko, 1988 (Sparsetooth dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53989&genusname=Scymnodalatias&speciesname=oligodon]
- Scymnodalatias sherwoodi (Archey, 1921) (Sherwood dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=698&genusname=Scymnodalatias&speciesname=sherwoodi]
- Scymnodon
- Scymnodon ichiharai Yano & Tanaka, 1984 (Japanese velvet dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53991&genusname=Scymnodon&speciesname=ichiharai]
- Scymnodon obscurus (Vaillant, 1888) (Smallmouth velvet dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=699&genusname=Scymnodon&speciesname=obscurus]
- Scymnodon ringens Barbosa du Bocage & Brito Capello, 1864 (Knifetooth dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=700&genusname=Scymnodon&speciesname=ringens]
- Scymnodon squamulosus (Günther, 1877) (Greenland sleeper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=701&genusname=Scymnodon&speciesname=squamulosus]
- Somniosus
- Somniosus microcephalus (Bloch & Schneider, 1801) (Sleeper shark, Greenland shark or Gurry shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=138&genusname=Somniosus&speciesname=microcephalus]
- Somniosus pacificus Bigelow & Schroeder, 1944 (Pacific sleeper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=2544&genusname=Somniosus&speciesname=pacificus]
- Somniosus rostratus (Risso, 1827) (Little sleeper shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=704&genusname=Somniosus&speciesname=rostratus]
- Squaliolus
- Squaliolus aliae Teng, 1959 (Smalleye pygmy shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=27208&genusname=Squaliolus&speciesname=aliae]
- Squaliolus laticaudus Smith & Radcliffe, 1912 (Spined pygmy shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=705&genusname=Squaliolus&speciesname=laticaudus] Family Squalidae
- Squalus
- Squalus acanthias Linnaeus, 1758 (Piked dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=139&genusname=Squalus&speciesname=acanthias]
- Squalus acutirostris Chu, Meng & Li, 1984 () [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53929&genusname=Squalus&speciesname=acutirostris]
- Squalus asper (Merrett, 1973) (Roughskin spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=707&genusname=Cirrhigaleus&speciesname=asper]
- Squalus blainville (Risso, 1827) (Longnose spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=708&genusname=Squalus&speciesname=blainville]
- Squalus cubensis Howell Rivero, 1936 (Cuban dogfish) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=709&genusname=Squalus&speciesname=cubensis]
- Squalus japonicus Ishikawa, 1908 (Japanese spurdog or Japanese roughshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=710&genusname=Squalus&speciesname=japonicus]
- Squalus magalops (Macleay, 1881) (Shortnose spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=711&genusname=Squalus&speciesname=megalops]
- Squalus melanurus Fourmanoir & Rivaton, 1979 (Blacktail spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=712&genusname=Squalus&speciesname=melanurus]
- Squalus mitsukurii Jordan & Snyder, 1903 (Shortspine spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=713&genusname=Squalus&speciesname=mitsukurii]
- Squalus rancureli Fourmanoir & Rivaton, 1979 (Cyrano spurdog) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=714&genusname=Squalus&speciesname=rancureli] Category:Sharks

Squatiniformes

(16 species, see text) The angel sharks are an unusual group of sharks, with their flattened bodies and broad pectoral fins that give them a strong resemblance to skates and rays. The 16-odd known species are all classified in a single genus Squatina belonging to its own family Squatinidae and order Squatiniformes. They occur worldwide in temperate and tropical seas. While the forward part of the body is broad and flattened, the rear part retains a muscular appearance more typical of other sharks. The eyes and spiracles are on top, and the five gill slits are on bottom. Both the pectorals are the pelvic fins are large and held horizontally. There are two dorsal fins, no anal fin, and unusually for sharks, the lower lobe of the caudal fin is longer than the upper lobe. Most types grow to a length of 1.5 meters (5 ft), with the Japanese angel shark Squatina japonica known to reach 2 meters. Angel sharks are bottom-dwellers, burying themselves in sand or mud, then lunging to snap up prey, which includes fish, crustaceans, and various types of mollusks. The Pacific angel shark Squatina californica is also known to leave the bottom at night to forage. Although they are not normally aggressive, they do bite when stepped on or handled. Angel sharks are ovoviviparous, with litters known up to 13 pups. The sharks were long considered of no commercial interest, but in 1978, Michael Wagner, a fish processor in Santa Barbara, California began to promote angel sharks, and 310 metric tons were taken off California in 1984. The fishery devastated the population, and is now regulated.

Species

- Squatina aculeata Cuvier, 1829 (Sawback angel shark), 188 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=725&genusname=Squatina&speciesname=aculeata]
- Squatina africana Regan, 1908 (African angel shark), 80 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=726&genusname=Squatina&speciesname=africana]
- Squatina argentina (Marini, 1930) (Argentine angel shark), 170 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=727&genusname=Squatina&speciesname=argentina]
- Squatina australis Regan, 1906 (Australian angel shark), 152 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=728&genusname=Squatina&speciesname=australis]
- Squatina californica 'Ayres, 1859 (Pacific angel shark), 152 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=729&genusname=Squatina&speciesname=californica]
- Squatina dumeril Lesueur, 1818 (Sand devil), 152 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=731&genusname=Squatina&speciesname=dumeril]
- Squatina formosa Shen & Ting, 1972 (Taiwan angel shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=732&genusname=Squatina&speciesname=formosa]
- Squatina guggenheim Marini, 1936 (Angular angel shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53932&genusname=Squatina&speciesname=guggenheim]
- Squatina japonica Bleeker, 1858 (Japanese angel shark), 200 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=733&genusname=Squatina&speciesname=japonica]
- Squatina nebulosa Regan, 1906 (Clouded angel shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=734&genusname=Squatina&speciesname=nebulosa]
- Squatina occulta Vooren & da Silva, 1992 (Smoothback angel shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=53931&genusname=Squatina&speciesname=occulta]
- Squatina punctata Marini, 1936 [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=62087&genusname=Squatina&speciesname=punctata]
- Squatina squatina (Linnaeus, 1758), 183 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=736&genusname=Squatina&speciesname=squatina]
- Squatina tergocellata McCulloch, 1914 (Ornate angel shark), 100 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=737&genusname=Squatina&speciesname=tergocellata]
- Squatina tergocellatoides Chen, 1963 (Ocellated angel shark), 63 cm [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=738&genusname=Squatina&speciesname=tergocellatoides]

External links

- [http://www.elasmo-research.org/education/shark_profiles/squatiniformes.htm Reefquest page on angel sharks]
- [http://www.mbayaq.org/efc/living_species/default.asp?hOri=1&inhab=484 Monterey Bay Aquarium page on Pacific angel shark] Category:Sharks

Heterodontiformes

See text. The bullhead sharks are a small order (Heterodontiformes) of very basal (primitive) modern sharks (Neoselachii). There are eight living species in a single genus, Heterodontus, in the family Heterodontidae. All are relatively small (50 to 150 cm) bottom feeders in tropical and subtropical waters. The symbol '$' below indicates a synapomorphy, (a character believed to be uniquely present in the last common ancestor of all heterodontiforms). The heterodontiforms are morphologically rather distinctive. The mouth is located entirely anterior to the orbits. Labial cartilages are found in the most anterior part of the mouth. Nasoral grooves are present, connecting the external nares to the mouth. The nasal capsules are "trumpet-shaped" & well-separated from orbits. $ Circumnarial skin folds present; but $ the rostral process of neurocranium (braincase) absent, although a precerebral fossa is present. Finally, the braincase bears a supraorbital crest. The eyes lack a nictitating fold. A spiracle is present, but small. The dorsal ends of branchial arches 4 and 5 are attached, but not fused into a "pickaxe" as in lamniform sharks. Heterodontiforms have 2 dorsal fins, with fin spines, as well as an anal fin. The dorsal and anal fin also contain basal cartilages, not just fin rays. The Heterodontiforms appear in the fossil record in the Early Jurassic, well before any of the other Galeomorphii, a group which includes all modern sharks except the dogfish and its relatives. However, they have never been common, and it is likely their origin lies even further back.

Classification

The genus Heterodontus contains eight species:
- Heterodontus francisci (Girard, 1855) (Horn shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=739&genusname=Heterodontus&speciesname=francisci]
- Heterodontus galeatus (Günther, 1870) (Crested Bullhead Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=740&genusname=Heterodontus&speciesname=galeatus]
- Heterodontus japonicus Maclay & Macleay, 1884 (Japanese Bullhead Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=741&genusname=Heterodontus&speciesname=japonicus]
- Heterodontus mexicanus Taylor & Castro-Aguirre, 1972 (Mexican Hornshark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=742&genusname=Heterodontus&speciesname=mexicanus]
- Heterodontus portusjacksonj (Meyer, 1793) (Port Jackson Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=743&genusname=Heterodontus&speciesname=portusjacksoni]
- Heterodontus quoyi (Fréminville, 1840) (Galapagos Bullhead Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=744&genusname=Heterodontus&speciesname=quoyi]
- Heterodontus ramalheira (Smith, 1949) (Whitespotted Bullhead Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=745&genusname=Heterodontus&speciesname=ramalheira]
- Heterodontus zebra (Gray, 1831) (Zebra Bullhead Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=746&genusname=Heterodontus&speciesname=zebra] Category:Sharks

Carcharhiniformes

Scyliorhinidae (cat sharks)
Proscyllidae (finback cat sharks)
Pseudotriakidae (false cat sharks)
Leptochariidae (barbeled houndshark)
Triakidae (hound sharks)
Hemigaleidae (weasel sharks)
Carcharhinidae (requiem sharks) The ground sharks, order Carcharhiniformes, are the largest order of sharks; they are also called whaler sharks. With over 270 species, carcharhiniforms include a number of common types, such as the blue shark and sandbar shark. Members of the orders are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin, and five gill slits. The families of the carcharhiniforms are expected to be revised; recent DNA studies show that some of the traditional groups are not monophyletic.

Taxonomy

- List of species of the order Carcharhiniformes

External link

- [http://www.elasmo-research.org/education/shark_profiles/carcharhiniformes.htm Order Carcharhiniformes] Category:Sharks

Lamniformes

- Odontaspididae (sand tigers)
- Mitsukurinidae (goblin shark)
- Pseudocarchariidae (crocodile shark)
- Megachasmidae (megamouth shark)
- Alopiidae (thresher sharks)
- Cetorhinidae (basking shark)
- Lamnidae (mackerel sharks) Lamniformes is an order of sharks. It includes some of the most familiar species of sharks, such as the Great White Shark, and some extremely rare types, such as the Megamouth Shark. Characteristics of the order include: two dorsal fins, an anal fin, five gill slits, eyes without nictitating membrane, and mouth extending behind the eyes.

Classification

Family Odontaspididae
- Carcharias
- Carcharias taurus Rafinesque, 1810 (Grey Nurse Shark or Sand tiger shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=747&genusname=Carcharias&speciesname=taurus]
- Carcharias tricuspidatus Day, 1878 (Indian sand tiger) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=748&genusname=Carcharias&speciesname=tricuspidatus]
- Odontaspis
- Odontaspis ferox (Risso, 1810) (Smalltooth sand tiger or bumpytail raggedtooth) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=749&genusname=Odontaspis&speciesname=ferox]
- Odontaspis noronhai (Maul, 1955) (Bigeye sand tiger) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=750&genusname=Odontaspis&speciesname=noronhai] Family Pseudicarchariidae
- Pseudocarcharias
- Pseudocarcharias kamoharai (Matsubara, 1936) (Crocodile shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5923&genusname=Pseudocarcharias&speciesname=kamoharai] Family Mitsukurinidae
- Mitsukurina
- Mitsukurina owstoni Jordan, 1898 (Goblin shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5910&genusname=Mitsukurina&speciesname=owstoni] Family Megachasmidae
- Megachasma
- Megachasma pelagios Taylor, Compagno & Struhsaker, 1983 (Megamouth Shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5909&genusname=Megachasma&speciesname=pelagios] Family Alopiidae
- Alopias
- Alopias pelagicus Nakamura, 1935 (Pelagic thresher) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=5891&genusname=Alopias&speciesname=pelagicus]
- Alopias superciliosus (Lowe, 1841) (Bigeye thresher) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=2534&genusname=Alopias&speciesname=superciliosus]
- Alopias vulpinus (Bonnaterre, 1788) (Thintail thresher) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=2535&genusname=Alopias&speciesname=vulpinus] Family Cetorhinidae
- Cetorhinus
- Cetorhinus maximus (Gunnerus, 1765) (Basking shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=90&genusname=Cetorhinus&speciesname=maximus] Family Lamnidae
- Carcharodon
- Carcharodon carcharias (Linnaeus, 1758) (Great white shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=751&genusname=Carcharodon&speciesname=carcharias]
- Isurus
- Isurus oxyrinchus Rafinesque, 1810 (Shortfin mako) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=752&genusname=Isurus&speciesname=oxyrinchus]
- Isurus paucus Guitart Manday, 1966 (Longfin mako) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=753&genusname=Isurus&speciesname=paucus]
- Lamna
- Lamna ditropis Hubbs & Follett, 1947 (Salmon shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=755&genusname=Lamna&speciesname=ditropis]
- Lamna nasus (Bonnaterre, 1788) (Porbeagle shark) [http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=88&genusname=Lamna&speciesname=nasus] Category:Sharks ko:악상어목

Fish

Conodonta
Hyperoartia
:Petromyzontidae (lampreys)
Pteraspidomorphi (early jawless fish)
Thelodonti
Anaspida
Cephalaspidomorphi (early jawless fish)
:Galeaspida
:Pituriaspida
:Osteostraci
Gnathostomata (jawed vertebrates)
:Placodermi
:Chondrichthyes (cartilaginous fish)
:Acanthodii
:Osteichthyes (bony fish)
::Actinopterygii (ray-finned fish)
::Sarcopterygii (lobe-finned fish)
:::Actinistia (coelacanths)
:::Dipnoi (lungfish)
A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fish (class Osteichthyes). Fish come in different sizes, from the 14m (45 ft) whale shark to a 7 mm (just over 1/4 of an inch) long stout infantfish. Many types of aquatic animals named "fish", such as jellyfish and cuttlefish, are not true fish. Other sea dwelling creatures, like dolphins, are actually mammals. Certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.

Fish ecology

Fish can be found in almost all large bodies of water in either salt, brackish, or fresh water, at depths ranging from just below the surface to several thousand meters. However, hyper-saline lakes like the Great Salt Lake do not support fishes. Some species of fish have been specially bred to be kept and displayed in an aquarium, and can survive in the home environment. Catching fish for the purpose of food or sport is known as fishing. The annual yield from all fisheries worldwide is about 100 million tonnes. Overfishing is a threat to many species of fish. On May 15 2003, the journal Nature reported that all large oceanic fish species worldwide had been so systematically over caught that fewer than 10% of 1950 levels remained. [http://www.globeandmail.com/servlet/story/RTGAM.20030514.wfish1405/BNStory/National/] Particularly imperiled were sharks, Atlantic cod, Bluefin tuna, and Pacific sardines. The authors recommended immediate, drastic cutbacks in fish catches and reservation of ocean habitats worldwide.

Note on usage: "fish" vs. "fishes"

"Fishes" is the proper English plural form of "fish" that biologists use when speaking about two or more fish species, as in "There are over 25,000 fishes in the world" (meaning that there are over 25,000 fish species in the world). When speaking of two or more individual fish organisms, then the word "fish" is used, as in "There are several million fish of the species Gadus morhua" (meaning that G. morhua comprises several million individuals). To see both in action, consider the statement "There are twelve fish in this aquarium, representing five fishes" (meaning that the aquarium contains twelve individuals, some of the same species and some of different species, for a total of five species). The usage of the two words is similar to that of the words "people" and "peoples".

Fish as food

Fishes are an important source of food in many cultures. Other water-dwelling animals such as mollusks, crustaceans, and shellfish are often called "fish" when used as food. For more details, see Fish (food). Fish (food)

External links

- [http://www.70south.com/resources/animals/marine/antarcticfish 70South - information on Antarctic fish]
- [http://www.aworldoffish.com A World of Fish] Species information and fish care
- [http://www.fishbase.org Fish database] (FishBase)
- Join Ray Mullet in the [http://www.liverpoolmuseums.org.uk/nof/fish/ Fish Olympics]!
- Project for children - [http://marine.rutgers.edu/~kils/BASS/mobile/INDEX.HTM build a fish mobile with a behavior]
- [http://www.aquatichouse.com Fish Keeping]
- [http://www.aquaticcommunity.com Site with one of the largest fish databases in the world]
- [http://reelinthefish.net/interviews/jameskoliver.html Reelinthefish.net | Interview with Dr James K. Oliver, Reefbase Scientist]
- [http://fishy.us Fishy.Us]Articles & Particles
- [http://hardrockforums.com/forums Saltwater & Freshwater Forums]
- [http://www.fishfriend.com/ Your Fish Tank's Friend]
- [http://find-a-seafood-recipe.com/ Fish and Seafood Recipes]Cooking With Fish
- [http://www.easyreefer.com/ Reef aquarium community and learning center]
- [http://www.fiberi.de German Educator in Fisheries, Specialist in Fancy Goldfish and Fishhealth, with Forum and large Picture-Gallery]
- [http://www.freeonlinegames.com/play/3019.html]Interesting fish game.
- [http://www.sushifaq.com The Sushi FAQ - (the alt.food.sushi Usenet group FAQ) at SushiFAQ.com]
- [http://sushiotaku.blogspot.com/ The Sushi Otaku Blog] Category:Fisheries science Category:Seafood zh-min-nan:Hî ko:물고기 ms:Ikan ja:魚類 simple:Fish th:ปลา

Skeleton

In biology, the skeleton or skeletal system is the biological system providing support in living organisms. (By extension, non-biological outline structures such as gantries or buildings may also acquire skeletons.) Skeletal systems are commonly divided into three types - external (an exoskeleton), internal (an endoskeleton), and fluid based (a hydrostatic skeleton), though hydrostatic skeletal systems may be classified separately from the other two since they lack hardened support structures. Large external skeletal systems support proportionally less weight than endoskeletons of the same size, and thus many larger animals, such as the vertebrates, have internal skeletal systems. Examples of exoskeletons are found in arthropods, shellfish, and some insects: the skeleton forms a hard shell-like covering protecting the internal organs. The phyla arthropoda and mollusca both have exoskeletons. Since exoskeletons necessarily limit growth, phyla with exoskeletons have come up with various solutions. Most molluscs have calcareous shells and as they grow, the diameter of the shell is enlarged without altering its shape. On the other hand, arthropods shed their exoskeletons to grow, a process known as molting (or ecdysis). During molting the arthropod breaks down their old exoskeleton and then regenerates a new one which they then harden through various processes (such as calcification or sclerotization). An internal skeletal system consists of rigid structures within the body, moved by the muscular system. If the structures are mineralized or ossified, as they are in humans and other mammals, they are referred to as bones. Cartilage is another common component of skeletal systems, supporting and supplementing the skeleton. The human ear and nose are shaped by cartilage. Some organisms have a skeleton consisting entirely of cartilage and without any calcified bones at all, for example sharks. The bones or other rigid structures are connected by ligaments and connected to the muscular system via tendons. Hydrostatic skeletons are similar to a water-filled balloon. Located internally in cnidarians (coral, jellyfish, etc.) and annelids (leeches), among others, these animals can move by contracting the muscles surrounding the fluid-filled pouch, creating pressure within the pouch that causes movement. Animals such as earthworms use their hydrostatic skeletons to change their body shape as they move forward from long and skinny to short and stumpy.

Gill

] In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. Many small aquatic animals absorb oxygen through the surface of their bodies in general, but more complex forms have localized respiratory organs formed to present an adequate surface area to the external environment. They are usually thin plates of tissue or slender tufted processes and, with the exception of some aquatic insects, they contain blood or coelomic fluid which exchange gases through their thin walls. In the insects a unique type of respiratory organ is used, the tracheal gill, which contains air tubes. The oxygen in these tubes is renewed through the gills. Gills are developed in sea stars and sea urchins (Echinoidea) as thin protuberances on the surface of the body containing diverticula of the water vascular system. In the crustaceans, molluscs and some insects, they are tufted or plate-like structures at the surface of the body in which blood circulates. The gills of other insects are of the tracheal kind and also include both thin plates and tufted structures, and in the larval dragon fly the wall of the caudal end of the alimentary tract (rectum) is richly supplied with tracheae as a rectal gill. Water pumped into and out of the rectum provide oxygen to the closed tracheae. Gills of vertebrates are developed in the walls of the pharynx along a series of gill slits opening to the exterior. Water taken into the mouth passes out of the slits, bathing the gills as it passes. Some fish utilize the gills for the excretion of electrolytes. In some amphibians the gills occupy the same position on the body but protrude as external tufts. In most species a countercurrent exchange system is employed to enhance the diffusion of substances in and out of the gill, with blood and water flowing in opposite directions to each other. The gill slits of fish are believed to be the evolutionary ancestors of the Eustachian tubes. Gills' large surface area tends to create a problem for fish seeking to regulate the osmolarity of their internal fluids. Saltwater is less dilute than these internal fluids; consequently, saltwater fish lose large quantities of water osmotically through their gills. To regain the water, they drink large amounts of seawater and excrete the salt. Conversely, freshwater is more dilute than the internal fluids of fish, so freshwater fish gain water osmotically through their gills. They eliminate the water through their urine. ----

Other Definition

- Gill (clan) is a gotra or surname found in the Jat community in India. ----

Head (anatomy)

:For other uses of the word head, see head (disambiguation). head (disambiguation) In anatomy, the head of an animal is the anterior part (from anatomical position) that comprises the mouth, the brain and various sensory organs (e.g. organs of sight, hearing, smell and taste).

Anatomy

The front (ventrum) of the head, where the deformed eyes and ears and wide opened mouth are located,it is called the ugly face of Mr.Head. The area above the eyes is called the forehead (the front of the head). Below the mouth is the chin. Younger aged humans and some older humans heads have a continuing growing layer of hair covering the head. Most females of the human race do not lose this covering during the aging process, however some males can lose their head hair as they grow older. Many animals have horns or tusks protruding from their head. In most complex animals the head is joined to the rest of the body by the neck.

Human head anatomy

Basic osteology

The bones of the human head is collectively called the skull. The skull is divided into the cranium (all the skull except the mandible) and the mandible or jawbone. One feature that distinguishes mammals and non mammals is that there are also three ear bones (called ossicles) -
- the malleus (hammer),
- incus (anvil),
- and stapes (stirrup). These ossicles are important components in the sense of hearing in mammals. Other animals have a single bone that is usually called the columella. The cranium can be divided into a calvarium (a skull cap) and a cranial base. The cranium consists of several bones which fuse together at junctions called sutures. This process occurs in utero to protect the most important organ in the body - the brain. Although most fusing is complete before birth, there are large areas where this in incomplete until puberty. These areas are called fontanelles and one particularly easily palpable one is present in the area just above the forehead in newborn babies and young children. Fontanelles are areas of fibrous tissue. The differentiated parts of the adult cranium are separated as
- 2 (one on each side of the head) maxillae. This bone covers an area inferior and medial (click anatomical position for explanations to what these terms mean) to the eye socket or orbit.
- 2 zygomatic bones, inferior and lateral to the orbit.
- 2 temporal bones, covering an area where the ears are located
- a frontal bone, superior to the orbit
- 2 parietal bones, posterior to the frontal bone and superior to the temporal bone
- an occipital bone at the back of the head
- several more internal bones which are not easily seen which are :
- a sphenoid :
- an ethmoid :
- 2 lacrimal bones :
- 2 nasal bones :
- 2 palatine bones :
- 2 nasal conchae (inferior) :
- a vomer an area where several sutures join up is called a pterion. The rest of the skull is the mandible, a bone attached to the cranium at the temporalmandibular joint (TMJ). This is an important joint which allows the mandible to move, using the TMJ as a pivot, and so achieve certain actions such as chewing (mastication), eating and speech. When viewed from below, (inferiorly), the skull contains several holes, by far the biggest of which is the foramen magnum, where the spinal cord passes through. Other holes allow for arteries, veins, and nerves (the cranial nerves) to pass through. When the skull cap or calvarium is removed the base of the skull is viewed from above, there are three clear impressions or fossa. The most anterior of these is the anterior cranial fossa, where, amongst other things, the frontal lobe of the brain would lie on. The middle cranial fossa is the second most anterior depression, shaped like a butterfly. The wings are where the temporal lobes of the brain lie. The body of the butterfly houses an important structure, the sella turcica(Latin, Turkish saddle), also know as the pituiary fossa or the hypophyseal fossa. This is where the pituitary gland, the major player in the endocrine system, rests. The posterior cranial fossa is where the foramen magnum is located and where the posterior lobe of the brain and the cerebellum lie.

The face

The face is anatomically considered to stretch from the point of the chin to the roots of hair. The skin is quite pliable and loose. Wounds tend to bleed quite freely as there is no deep fascia. There are five orifices on the face - the two eyes, the two nostrils and the mouth The blood supply to the face and indeed the most of the scalp comes mainly from the external carotid artery. The sensory supply to the face comes solely from the trigeminal nerve (fifth cranial nerve). There are three divisions to this nerve,
- the ophthalmic division, which covers an area superior to the eye, including the forehead and most of the nose.
- the maxillary division, which covers an area inferior to the eye but above the mouth, including the cheeks and some of the nose
- the mandibular division, which covers an area inferior to the mouth but also lateral to the cheeks all the way until the ears. This area does not cover the mandibular angle (the protrusion on the jawbone) The muscles in the face are:
- the frontal part of the occipitofrontalis muscle. This muscle is a large muscle which contains two parts, the occipital part and the frontal part (also just simply known as frontalis and occipitalis). Although the two muscles are separate and supplied by different nerves, they are connected by an aponeurosis (fibromuscular tissue) which stretches across the top half of the head and forms what is known as the scalp. The aponeurosis is also known as the galea aponeurotica, or aponeurosis of Galen and this arrangement of two different muscles attached together is called a digastric muscle. :-the muscle is attached to the skin of the forehead and eyebrow anteriorly and the superior nuchal line posteriorly. :-the muscle's frontal belly is supplied by the temporal nerve, a branch of the facial nerve (cranial nerve VII) and the occipital belly by the posterior auricular, also a branch of the facial nerve. :-the action of the muscle is to wrinkle the forehead and raise the eyebrow.
- Nasal muscles
- The mouth muscles
- Zygomatic muscles