Hexanchidae

Hexanchidae is a family of sharks commonly known as sixgill or sevengill sharks. These sharks are characterized by having six or seven gill slits on each side of their heads, a feature that distinguishes them from most other shark species which have five. They are ancient lineages, with fossil evidence dating back to the Jurassic period. Hexanchids are found in deep waters around the world, typically inhabiting continental slopes and seamounts.

There are currently three recognized genera within the Hexanchidae family: Hexanchus, Notorychus, and Heptranchias. The genus Hexanchus includes the bluntnose sixgill shark and the sharpnose sixgill shark. Notorychus contains the broadnose sevengill shark, and Heptranchias is represented by the sharp-tailed sevengill shark. These sharks are generally large, with some species reaching lengths of over 5 meters.

Hexanchid sharks are slow-moving predators, feeding on a variety of prey including fish, crustaceans, cephalopods, and carrion. Their dentition is heterodont, meaning they have different types of teeth, with large, comb-like lower teeth adapted for tearing flesh. Due to their deep-water habitat, encounters with humans are rare, and they are not considered a significant threat. Some species are caught as bycatch in fisheries, but their populations are not well-studied.