Bluntnose sixgill shark
| Bluntnose sixgill shark | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Superorder: | Selachimorpha |
| Order: | Hexanchiformes |
| Family: | Hexanchidae |
| Genus: | Hexanchus |
| Species: | H. griseus |
| Binomial name | |
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Hexanchus griseus (Bonnaterre, 1788) |
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| Range of bluntnose sixgill shark (in blue) | |
The bluntnose sixgill shark (Hexanchus griseus), often simply called the cow shark, is the largest hexanchoid shark, growing to 16 ft (4.9 m) in length. It is found in tropical and temperate waters worldwide and its diet is widely varied by region.
The first scientific description of the bluntnose sixgill shark was authored in 1788 by Pierre Joseph Bonnaterre. As a member of the Hexanchidae family, it has more close relatives in the fossil record than living relatives. The related living species include the dogfish, the Greenland shark, and other six- and sevengilled sharks. Some of the shark's relatives date back 200 million years. This shark is a notable species due to both its primitive and current physical characteristics.
The bluntnose sixgill shark has a large body and long tail. The snout is blunt and wide, and its eyes are small. There are 6 rows of saw-like teeth on its lower jaw and smaller teeth on its upper jaw. Skin color ranges from tan, through brown, to black. It has a light-colored lateral line down the sides and on the fins' edges, and darker colored spots on the sides. Its pupils are black and its eye color is a fluorescent blue-green. The bluntnose sixgill shark can grow to 8 m (26 ft). Adult males generally average between 3.1 and 3.3 m (10 and 11 ft), while adult females average between 3.5 and 4.2 m (11 and 14 ft).
The bluntnose sixgill shark resembles many of the fossil sharks from the Triassic period. A greater number of Hexanchus relatives occur in the fossil record than are alive today. They have one dorsal fin located near the caudal fin. The pectoral fins are broad, with rounded edges. The six gill slits give the shark its name. Most common sharks today only have five gill slits.
Jaws, male
Upper teeth, male
Upper teeth, female
Lower teeth, male
Lower teeth, female
With a global distribution in tropical and temperate waters, the bluntnose sixgill shark is found in a latitudinal range between 65°N and 48°S in the Atlantic, Indian, and Pacific oceans. It has been seen off the coasts of North and South America from North Carolina to Argentina and Alaska to Chile. In the eastern Atlantic it has been caught from Iceland to Namibia and in the Indo-Pacific it has been caught from Madagascar north to Japan and east to Hawaii. It typically swims near the ocean floor or in the water column over the continental shelf in poorly lit waters. It is usually found 180–1,100 m (590–3,610 ft) from the surface, but its depth range can extend from 0–2,500 m (0–8,202 ft). Juveniles will swim near the shoreline in search of food, sometimes in water as shallow as 12 m (39 ft), but adults typically stay at depths greater than 100 m (330 ft). It can be seen near the ocean's surface only at night.
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Wikipedia