Author: Gray, 1851
Field Marks:
Cylindrical sharks with 6 or 7 gill slits, subterminal mouth with large, bladelike, comb-shaped teeth in lower jaw, and one dorsal fin.
Diagnostic Features:
Body cylindrical and moderately slender to stout, without keels on abdomen. Head with 6 or 7 pairs of gill slits, the lower ends of the first gill slits not connected to each other across throat; snout short to moderately long, conical and slightly pointed to broadly rounded; mouth subterminal on snout, moderately long; teeth well-differentiated in upper and lower jaws, upper anterolaterals small, narrow, with a main cusp and often smaller cusplets, lowers very broad, compressed and sawlike, with a series of large cusplets and a short to elongated cusp; posterior teeth small and granular at corners of dental bands. Anal fin small, smaller than dorsal fin; caudal fin with a strong subterminal notch.
Habitat, Distribution and Biology:
Cow sharks have a worldwide distribution in boreal and cold temperate to tropical seas. Most species are deepwater inhabitants of the outer continental shelves, upper continental slopes, insular shelves and slopes, and submarine canyons down to at least 1875 m depth, near the bottom or well above it; but also occurring in shallow bays, close inshore, and near the surface. Behaviour of these sharks is poorly known: they are sluggish to active often strong-swimming sharks that occur near the bottom. They range in size from small to very large, with various species between 1.4 to 4.8 m maximum total length at maturity.
They feed on relatively large marine organisms, including other sharks, rays, a wide variety of bony fishes, crustaceans, and carrion (including mammalian meat). Cow sharks are ovoviviparous (aplacental viviparous), and lack a yolk-sac placenta.
These sharks are apparently not implicated in unprovoked attacks on swimmers and divers, though they may bite aggressively during capture and can inflict severe lacerations when handled. One species (broadnose sevengill shark) has attacked divers in aquarium display tanks and two of the cowsharks (broadnose sevengill and bluntnose sixgill sharks) reach sufficiently large size (from 2.9 to 4.7 m) to rank as potentially dangerous to people in the water.
Interest to Fisheries:
Cow sharks are relatively unimportant but regular components of shark fisheries and bycatches of other fisheries in temperate and tropical waters, and are taken by line gear, bottom and pelagic trawls, and gill nets. These sharks are excellent for human food and are utilized fresh and dried-salted; they are also processed for fishmeal, oil, and leather. Some species are subject to sports fisheries in shallow waters.
Remarks:
The genus Heptranchias is morphologically divergent from other members of Hexanchidae and has sometimes been placed in its own family, Heptranchidae (Compagno, 1973c).