Notorynchus

Notorynchus is a genus of cow shark in the family Hexanchidae. This genus is characterized by having six or seven gill slits on each side of the head, unlike most other sharks which have five. Currently, there are two recognized living species within the genus Notorynchus, though some historical species are also assigned to it.

The most well-known species is the sevengill cow shark, Notorynchus cepedianus. This species is found in temperate coastal waters of the Pacific and Atlantic Oceans, and is a large, robust shark that can reach lengths of over 3 meters. It has a broad, blunt head and a single dorsal fin located far back on its body. Its diet is varied, including fish, crustaceans, cephalopods, and even marine mammals. Another recognized species is the bluntnose sixgill shark, Notorynchus serratissimus, although its taxonomic status and distinction from N. cepedianus has been debated.

Fossil evidence suggests that Notorynchus has a long evolutionary history, with remains dating back to the Cretaceous period. These ancient cow sharks likely occupied similar ecological niches to their modern descendants. The genus's unique characteristic of multiple gill slits is considered a primitive trait among sharks. Conservation statuses for living species vary, with some populations facing threats from overfishing and habitat degradation.