hexanchid

The Hexanchidae family comprises a group of deep-sea sharks commonly known as cow sharks or bluntnose sharks. This family is part of the order Hexanchiformes, which is one of the most ancient lineages of sharks, dating back over 125 million years. Hexanchid sharks are characterized by their broad, rounded snouts, five gill slits (a unique feature among sharks), and relatively small size, typically ranging from 1 to 3 meters in length.

The family includes three genera: *Hexanchus*, *Notorynchus*, and *Heptranchias*. The broadnose sevengill shark (*Notorynchus cepedianus*) is the most well-known member, often encountered in temperate and tropical coastal waters worldwide. The other species, such as the Greenland shark (*Somniosus microcephalus*, sometimes loosely associated with Hexanchidae), are less frequently observed but inhabit even greater depths.

Hexanchid sharks are primarily found in deep waters, often exceeding 200 meters in depth, though some species venture into shallower regions. They are slow-moving, bottom-dwelling predators that feed on a variety of prey, including fish, cephalopods, and crustaceans. Their diet and behavior suggest a low metabolic rate, contributing to their longevity—some species, like the Greenland shark, are known to live over 400 years.

Reproduction in hexanchids is ovoviviparous, meaning embryos develop within eggs that remain inside the mother’s body until hatching. The pups are born fully formed and capable of immediate survival. Due to their deep-sea habitat and slow reproductive rates, hexanchid sharks are vulnerable to overfishing and habitat disturbance, though they are not currently classified as globally threatened.

These sharks play an ecological role in maintaining the balance of deep-sea ecosystems, and their study provides insights into the evolutionary history of sharks. Conservation efforts focus on sustainable fishing practices and protecting their habitats to ensure their long-term survival.