Scyliorhinus is a genus of catsharks in the family Scyliorhinidae. This genus is known in the fossil records from the Cretaceous period, late Albian age to the Pliocene epoch.
The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.
The Lamniformes are an order of sharks commonly known as mackerel sharks. It includes some of the most familiar species of sharks, such as the great white, as well as more unusual representatives, such as the goblin shark and megamouth shark.
The Lamnidae are the family of mackerel sharks known as white sharks. They are large, fast-swimming predatory fish found in oceans worldwide, though prefer environments with colder water. The name of the family is formed from the Greek word lamna, which means "fish of prey", and was derived from the Greek legendary creature, the Lamia.
The broadnose sevengill shark is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark. This shark has a large, thick body, with a broad head and blunt snout. The top jaw has jagged, cusped teeth and the bottom jaw has comb-shaped teeth. Its single dorsal fin is set far back along the spine towards the caudal fin, and is behind the pelvic fins. In this shark the upper caudal fin is much longer than the lower, and is slightly notched near the tip. Like many sharks, this sevengill is counter-shaded. Its dorsal surface is silver-gray to brown in order to blend with the dark water and substrate when viewed from above. In counter to this, its ventral surface is very pale, blending with the sunlit water when viewed from below. The body and fins are covered in a scattering of small black & white spots. In juveniles, their fins often have white margins.
The bluntnose sixgill shark, often simply called the cow shark, is the largest hexanchoid shark, growing to 20 ft (6.1 m) in length. It is found in tropical and temperate waters worldwide and its diet is widely varied by region.
The sharpnose sevengill shark, also known as one-finned shark, perlon shark, sevengill cow shark, sharpsnouted sevengill or slender sevengill, is a species of shark in the family Hexanchidae, and the only living species in the genus Heptranchias. Found almost circumglobally in deep water, it is one of the few species of sharks with seven pairs of gill slits as opposed to the usual five. The other shark species with seven gill slits is the broadnose sevengill shark. Though small, this shark is an active, voracious predator of invertebrates and fish. When caught, this species is notably defensive and will attempt to bite. It is of minor commercial importance.
Heptranchias is a genus of sharks in the family Hexanchidae.
The sixgill sharks are a genus, Hexanchus, of deepwater sharks in the family Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of gill slits, comb-like, yellow lower teeth, and a long tail. The largest species can grow up to 8 m long and weigh over 600 kg (1320 lb). They are continental shelf-dwelling and abyssal plain scavengers with a keen sense of smell and are among the first to arrive at carrion, together with hagfish and rattails. They show a characteristic rolling motion of the head when feeding.
Notorynchus is a genus of deepwater sharks in the family Hexanchidae. There is one extant species.
The bigeyed sixgill shark is a cow shark of the family Hexanchidae. Its dorsal surface has a brownish-gray color, and is sharply separated from the light coloring of its ventral surface. The eyes are a fluorescent green while the shark is alive. The body of this shark is small, slim, and fusiform in shape. As the name suggests, this shark has six gill slits, unusual among most shark species. The head is narrow and somewhat flattened, and the mouth contains 5 rows of large, comb-shaped teeth. This shark's single dorsal fin is pushed back towards the caudal fin, and is behind the pelvic fins. The upper caudal fin is much longer than the lower, with a deep notch near the tip. All fins have thin white margins on the edge. In juveniles, the upper caudal fin has a black tip.
Gladioserratus is an extinct genus of cow shark. It contains three species:
Welcommia is an extinct genus of shark. It contains only three species :-
Squalomorphii is a superorder of cartilaginous fishes, generally characterized by lacking traits such as an anal fin, nictitating membrane, or suborbital shelves in the cranium. Also called squalea, or squalean sharks. There are about 163 living species in 11 families. Squalean sharks are divided into four orders: the Hexanchiformes, Squaliformes, Squatiniformes, and Pristiophoriformes.
Pseudocorax is an extinct genus of mackerel sharks that lived during the Late Cretaceous. It contains six valid species that have been found in Europe, the Middle East, North Africa, and North America. It was formerly assigned to the family Anacoracidae, but is now placed in its own family Pseudocoracidae along with Galeocorax. The former species "P." australis and "P." primulus have been reidentified as species of Echinorhinus and Squalicorax, respectively.
Synechodontiformes is an extinct order of prehistoric sharks, known from the Permian to the Paleogene. They are considered to be members of Neoselachii, the group that contains modern sharks and rays. Their placement in the group is uncertain, some authors have considered them to be galeomorph crown-group sharks, while others have considered them to represent a stem-group to modern sharks. They have sometimes been considered a paraphyletic grouping, but Klug (2010) recovered the group as monophyletic. Members of the clade are united by two synapomorphies, "pseudopolyaulacorhize tooth root pattern present; labial root depression in basal view present". The oldest possible member of the clade are teeth from the early Permian (Cisuralian) of the Ural Mountains.
The Atlantic sixgill shark is a rare species of hexanchid shark found in the Atlantic Ocean at depths that are greater than 300 meters. These depths are known as mesopelagic and bathypelagic in tropical and temperate waters around the world. The Atlantic sixgill shark is very similar to other species of sixgill in terms of its growth rate in deep sea waters. It is believed that this is due to the abiotic and biotic factors in relation to the depths at which they are found. It was formerly described as its own species, but was synonymised with the bigeye sixgill shark. However, a study published in 2019 resurrected the species on the basis of molecular data. The species can be physically differentiated from the bluntnose sixgill shark by its much smaller size and position of the dorsal fin in relation to the caudal fin. The Atlantic sixgill shark becomes sexually mature at around 1.40 to 1.75 meters. They do not reach lengths much greater than 180 cm.
Notidanodon is an extinct genus of cow shark. Fossils ascribed to this genus are known from the Jurassic, Cretaceous, and Paleogene periods. The genus is known from every continent including Antarctica.
