Chondrichthyes (//; from Greek χονδρ- chondr- 'cartilage', ἰχθύς ichthys 'fish') or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).
The Galápagos fur seal (Arctocephalus galapagoensis) breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.
The bluntnose sixgill shark, Hexanchus griseus, often simply called the cow shark, is the largest hexanchoid shark, growing to 4.8 m (16 ft) in length. This shark is one of the commonly studied deep-sea sharks due to students using bait (tuna or carrion) to do tests to see how deep-sea fish find their food in the lightless world of the deep sea.
The bluntnose sixgill shark is a member of the Hexanchidae family. Many of its relatives are extinct - there are more closely related relatives in the fossil record than there are living species. The living species that are closest genetically include the dogfish, the Greenland shark, as well as other six- and sevengilled sharks. Some of the shark's relatives date back to 200 million years ago. This shark is a notable species due to both its primitive and current physical characteristics.