The most primitive of all types of sharks, the cow sharks are scientifically known as Hexanchidae. This family of fish consists of four separate species. They are characterized by very simple digestive and excretory systems, a preference for mostly warm, deep seas, and extra pairs of gill slits. While most sharks have five gill slit pairs, these sharks have either six or seven.
Cow shark skeletons are very simple, resembling the body structures of similar but extinct animals. Unlike many other types of sharks, Hexanchidae feature very few adaptations to the modern world. Their excretory and digestive systems are not specialized like most contemporary species, which also signifies a relationship to primitive species.
Gray or brown upper parts are featured on most cow sharks. Their underbellies are typically a slightly lighter shade. The animals also feature a stout body, a single dorsal fin and a single anal fin, as well as sharp, thorn-like teeth. Sevengill Cow Sharks are also known as the wolves of the sea.
Hexanchidae can range from nearly five feet (one and one-half meters) to 18 feet (five and one-half meters) in length. Ovoviviparous fish, cow shark females carry their eggs until they hatch. The cow shark's diet ranges from crustaceans and carrion to all different sorts of fish, including different shark species.
Four separate species make up the cow shark family. The Genera Heptranchias, or Sharpnose Sevengill Shark, has seven gills, as does the Genera Notorynchus, or Broadnose Sevengill Shark. The former is a small but aggressive fish found in deep water in tropical and temperate zones. The latter can grow to be very large, up to 10 feet (300 centimeters) in length, and has been known to attack humans.
Genera Hexanchus, which has six gills, consists of two species: the Bluntnose and Bigeye Sixgill sharks. Unlike the other two species, these two sharks are less aggressive, and have not been known to attack humans. Both prefer deep waters that measure at least 300 feet (90 meters) in depth or more.
Habitat ranges for cow sharks are very wide. The fish live in the Atlantic, Pacific, and Indian Oceans. Usually they can be seen in slope waters, as well as the continental shelf. The fish prefer muddy, sandy waters as well as rocky areas. In South Africa, the sharks occupy False Bay, a Marine Protected Area. No other conservation projects are used to protect the cow shark.
Sometimes they venture into shallow coastline waters, where they can be seen by humans. Humans should avoid contact with the sharks, as some species do attack. The cow shark is commercially fished in some areas, including the United States, China, and Australia. It is used as a food source as well as its skin, which is sold as a leather product.