The Bigeyed Sixgill Shark is a cow shark of the family Hexanchidae. They are listed as DD (Data Deficient) by the IUCN Red List. Based on what little we know of the species, it is thought that these sharks are not suffering major hits to their population, but that there is a growing pressure from deepwater fisheries. More research is necessary to determine a specific IUCN rating. According to the International Shark Attack File, the bigeyed sixgill is harmless, as its natural environment is far from people, and there have been no recorded attacks on humans by the species.
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.
These sharks live near the sea floor between 90m and 600m, but may move closer to the surface at night to take advantage of the food that gathers there. They make their home on continental shelves, insular shelves, and upper slopes. These sharks do not inhabit abyssal environments.
Little is known about the feeding habits of the bigeyed sixgill. It is thought, based on the few stomach examinations of these sharks, that they mainly feed on small to moderately-sized bony fish and crustaceans. Like all sharks of the order Hexanchiformes found so far, this shark is ovoviviparous, meaning that the eggs are retained inside the body until hatching. The bigeyed sixgill, after an unknown gestation period, gives birth to litters of up to 13 pups. It is very possible, because of the size of this shark, that their main predators are larger sharks.