Hexanchus

Hexanchus is a genus of deep-sea sharks belonging to the family Hexanchidae, commonly known as cow sharks or bluntnose sixgill sharks. The genus contains two recognized species: Hexanchus griseus, the bluntnose sixgill shark, and Hexanchus nakamurai, the bigeyed sixgill shark. These sharks are notable for possessing six gill slits, a characteristic shared with their close relatives in the Hexanchidae family, distinguishing them from most other shark species which typically have five.

Bluntnose sixgill sharks (Hexanchus griseus) are among the largest species in the Hexanchidae family, often reaching lengths of up to 6 meters (20 feet). They are found in temperate and tropical waters worldwide, inhabiting depths ranging from the surface to over 1,000 meters (3,300 feet). These sharks have a robust, cylindrical body, a broad, blunt snout, and a long, whip-like tail. Their coloration is typically grayish-brown dorsally, fading to white ventrally, which aids in camouflage against the ocean floor. They are slow-moving predators, primarily feeding on bony fishes, rays, and other sharks, though they are not considered aggressive toward humans.

Bigeyed sixgill sharks (Hexanchus nakamurai) are smaller, generally reaching lengths of about 3 meters (10 feet). They are primarily found in the western Pacific Ocean, particularly around Japan and the Philippines, though they have also been recorded in other parts of the Indo-Pacific region. Like their larger relative, they possess six gill slits and a blunt snout, but they are distinguished by their larger eyes, which give them their common name. Bigeyed sixgill sharks inhabit deep waters, often between 200 and 1,000 meters (660 and 3,300 feet), and feed on a similar diet of bony fishes and invertebrates.

Both species are ovoviviparous, meaning they give birth to live young that develop within eggs inside the mother’s body. Hexanchus sharks play an important role in deep-sea ecosystems, and while they are not heavily targeted by commercial fisheries, they are occasionally caught as bycatch. Due to their slow reproductive rates and deep-water habitats, they are considered vulnerable to overfishing and habitat degradation, though specific conservation statuses vary by species and region.