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The Sevengill shark

Hexanchidae sharks, genus Heptranchias, genus Notorynchus, Hexanchidae family

Heptranchiasperlo- The sharpnose sevengill shark

Notorynchuscepedianus - The broadnose sevengill shark

Sevengill sharks, as well as sixgill ones, belong to Hexanchiforme order of Hexanchidae family. They are represented by two genera: sharpnose sevengill and broadnose sevengill sharks. As one may guess, these two species have their names according to the number of gills they have on each side. Unlike other sharks, which have five pairs of gills slits, the sharks of Hexanchidae family (griset sharks) have either six (sixgill) or seven (sevengill) pairs of gill slits.

Theres also one sixgill species among saw sharks, but according to its constitution it still belongs to Pristiophoridae family (saw sharks).

The word Hexanchidae can be literally translated from Latin as cow fish. Cow sharks as some predatoryrepresentatives of this family are often called have a fusiform body with a single dorsal fin, which is situated not far from the caudal fin and pretty much under the anal fin.

They have an even coloration and a nearly equal color of belly and back. Their color may vary from dark brown to grey. Their eyes are green and can fluoresce in the dark.

The dentition of the sevengill shark has a unique structure, due to which the whole family got its name. The shape of the teeth on the lower row looks similar to a cockscomb: theyre sharp, curved inwardly and of different height. Thanks to such a structure these sharks can not only hold easily any slick prey, but to crack a crab crust as well.

All the cow sharks are regarded as the eldest representatives of all the predator fishwhich have come to our days. There is reliable scientific information proving the fact that these sharks have been existing at least since Mesozoic era.The archeologists have found some fossil remains of such shark in the deposits of Jurassic age. Therefore, cow sharks turned out to be dwelling the ancient seas about 150 million years ago.

These are quite primitive creatures with their bodies having all the main features of the eldest species. The scientists have discovered a lot of different shark species so far, but any of them looks so similar to its ancient fellows as the cow sharks do.

Unlike other Hexanchiformes, sevengill sharks live at a depth of about 500 meters. This gave the marine biologists an opportunity to study their behavior very thoroughly.  The scientists currently know only two species of sevengill sharks:Notorynchuscepedianus the broadnose sevengill shark and Heptranchiasperlo the sharpnose sevengill shark.

Sevengill shark habitats

Both species of sevengill sharks inhabit the American coastal waters. The broadnose sevengill shark dwells next to the Cuban shores and in the Atlantic Ocean, while the sharpnose one lives in Pacific Ocean and all over South America coast waters. The sevengill sharks can also be met nearby the shores of Spain, South Africa, Japan, Australia, and in the Mediterranean sea.

The sevengill sharks feed on gastropods, crabs, octopuses, small sharks, guitarfish, stone eels and many species of bony fish: sturgeon, salmon, anchovy and others. They dont loath eating carrion too, as well as rats, which get to the ocean from desert islands, where they live in large populations.

The sevengill sharks inhabiting the coastal waters at the south of Africa feed on squids, crustaceans,lamellibranchiate and bony fish representatives. At times they may go hunting on dolphins and fur seals, their favorite large prey.

Sevengill sharks are ovoviviparous. Their males become pubescent as they get their bodies around 1,5 meters long; females when they are 1,8 - 2 meters long. They usually produce more than 100 individuals per spawn. The shark pups are born 50 centimeters long and quite adapted to the individual life style; they grow very fast.

Notorynchusplatycephalus. The broadnose sevengill shark.

The Broadnose sevengill shark is a pretty large representative of the sevengill sharks. Its length can reach up to 2 meters, with its average weight around 250 kilograms. Its main difference from other shark species lays in an additional pair of gills it has on each side. It has one dorsal fin not far from the caudal fin, and big eyes without nictitating membranes.

The broadnose sevengill sharks live at a depth within 300 and 500 meters under the surface. They prefer to dwell in creeks and gulfs. They rise to the surface during daytime and go back to the bottom at night. In other words, they make a diurnal migration. These predators also make seasonal migrations. In warm seasons they prefer to dwell in shallow waters, in cold seasons they go depthward following the plankton, which is a perfect food for fish and animals. The sharks themselves feed on the latter.

The broadnose sevengill shark hunts various marine fauna representatives: stone eels, smaller sharks, fish eggs, snails, bony fish, ghost sharks and rats. It also feeds on porpoises, dolphins and seals.

From the earliest times, the broadnose sevengill shark is considered one of the most precious fishery subjects. The Maori hunters used to make special tools like saws for human meat from sharp tuatini teeth (their name for the broadnose sharks). They used the shark oil mixed with sienna to paint their boats and the great leaders funeral stones too. They also used the oil to grease the heads and bodies of their dead.

Nowadays the broadnose sevengill sharks are mostly harvested in Shandong and Liaoning provinces of China. They are caught with hooks instead of nets. Their liver contains 75% of oil, exceedingly rich in vitamin A. For comparison, other sharks liver contains only 14 to 25% of oil. The broadnose sevengill shark oil is widely used in Chinese medical practice and pharmacology.

But Europeans only use the broadnose sharks for food. Furthermore, they eat all the parts of it: from its body to the fins; and even the skin. The broadnose shark meat is very popular in south California. Its liver, as well as the whales one, is quite risky to eat because of great number of vitamins it contains. Havingenjoyed it once, one may get poisoned from their overuse.

Some of the broadnose sevengill sharks are really dangerous for humans. There are some 3 to 4,5 meters long man-eaters dwelling next to South America, America, Australia shores, or in the Mediterranean sea, who have attacked humans for many times.

Heptranchiasperlo.The sharpnose sevengill shark.

The sharpnose sevengill shark belongs to the second known species of the sevengill sharks. The upper part of its body is brown-grey; its belly is light brown. The sharpnose shark can also be called slender sevengill shark, one-finned shark, and sevengill cow shark.

Thanks to the unique shape of its body the sharpnose shark is an excellent swimmer. It has a narrow, pointed head and slim, streamline body. It can hold easily its prey, squids and fish with its sharp teeth. The big eyes of sharpnose shark let it hunt at a depth about one kilometer, while other sharks usually stay in shallow waters up to 500 meters.

The sharpnose sevengill shark prefers tropical and temperate waters of the Atlantic Ocean. They dwell next to the coasts of Cuba, Spain, South Africa, and also in the Mediterranean Sea.

The sharpnose sevengill shark is an ovoviviparous fish. The females can bring forth under 20 pups per turn. Comparing to other shark species the sharpnose sharks have pretty modest size: about 1,3 meters. Thats why this species isnt regarded as too dangerous for humans. Nevertheless, they are quite aggressive, which one may clearly observe having caught one of them. And this is the very reason by which the sharpnose shark is,however, included to the rank of dangerous ones. In addition, the sharpnose sevengill shark can be even more dangerous than whale shark, or basking shark, as it can inflict severe injuries with its teeth.

There is an instance when the sharpnose sevengill shark, kept in captivity, has violently attacked the diver. It is guilty for petty attacks on people in shallow waters too. Once upon a time there were found some human remains in the stomach of one of the sharpnose sharks. But it is still unknown, whether the predator has hunted someone down, or simply was feeding on the already dead body.

There also was an incident in 2010, when the sharpnose sevengill shark attacked a teenage girl next to the shores of New Zealand. Fortunately, the girl has managed to hurl it back with her bodyboard. Butstill, she had her leg bitten and was taken to the hospital. After that the girl, who used to be very keen on sea sports,has given up swimming in the ocean. A year before there already was registeredseveralsimilar incidents. One of such sharpnose shark victims has got 60 stitches.

Yet, the sharpnose sevengill shark is less aggressive than, say, the bullhead shark or the great white shark. Nevertheless, one shouldnt relax while bathing in the areas the sharpnose sharks supposedly dwell.

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