(Hexanchidae)
Cow Sharks
Багатозяброві акули
Cow sharks are considered the most primitive of all the sharks, as their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialized, suggesting they may resemble those of primitive shark ancestors. A possible hexanchid tooth is known from the Permian of Japan, making the family a possible extant survivor of the Permian–Triassic extinction.
Their most distinctive feature, however, is the presence of a sixth, and, in two genera, a seventh, gill slit, in contrast to the five found in all other sharks. The first pair are not connected across the throat. They range from 1.4 to 5.5 m in adult body length.
These cylindrical sharks have a ventral mouth with compressed, comb-like teeth in the lower jaw and smaller, pointed teeth in the upper jaw. They have a short, angular and spinless dorsal fin. The pelvic fins are smaller than the angular pectoral fins. The caudal fin has a notch towards the end.
Cow sharks are ovoviviparous, with the mother retaining the egg cases in her body until they hatch. They feed on relatively large fish of all kinds, including other sharks, as well as on crustaceans and carrion.
The International Shark Attack File considers the Broadnose Sevengill Shark (Notorynchus cepedianus) to be potentially dangerous because of its proximity to humans, and because of its aggressive behavior when provoked.
(Heptranchias perlo)
Sharpnose Sevengill Shark
Семизяброва акула гостроноса
It is uncommon, but widely distributed in the tropical and temperate regions of all oceans except for the north-eastern Pacific Ocean. It is mainly found on the outer continental shelf and upper continental slope, and may aggregate around seamounts, at depths from the surface to 1,000 m.
(Hexanchus griseus)
Bluntnose Sixgill Shark
Акула шестизяброва
It has a global distribution in tropical and temperate waters, occurring between 65°N and 48°S in the Atlantic Ocean, Indian Ocean, and Pacific Ocean. It typically swims near the ocean floor or in the water column over the continental shelf in poorly lit waters, at depths of 0–2,500 m.
(Hexanchus nakamurai)
Bigeye Sixgill Shark
Шестизяброва акула великоока
It is found in the Indian Ocean and the western Pacific Ocean. It lives near the seafloor at depths of 90–600 m.
(Hexanchus vitulus)
Atlantic Sixgill Shark
Шестизяброва акула атлантична
It inhabits tropical waters across the Gulf of Mexico and the Caribbean Sea in the Atlantic Ocean. It is found from the surface to as deep as 700 m.
(Notorynchus cepedianus)
Broadnose Sevengill Shark
Семизяброва акула широконоса
It is found in the western Pacific Ocean off China, Japan, Australia, New Zealand, the eastern Pacific Ocean off Canada, United States and Chile, and the southern Atlantic Ocean off Argentina and South Africa. It occurs from the surface to depths of 300–570 m and is often found in bays and estuaries.
