Shark a common name for any fish of the group Selachoidei [FISHES], widely distributed. but most numerous between the tropics. The body is long and cylindrical, with a pointed snout, and strong flexible tail, the latter forming an admirable swimming organ. In the place of scales the skin is covered with calcified papillae; the teeth are well developed in most forms, though in some they are adapted for crushing rather than cutting, and these sharks feed only on small fish or on molluscs and crustaceans. In most the eggs are enclosed in a horny case, though some bring forth the young alive. In India and China the collecting of sharks' fins is an important industry. They are used for making a thick gelatinous soup. In Ceylon a shark fishery is carried on, and oil is expressed from the livers. The skin is also utilised for shagreen. Dr. Gunther (Introduction to the Study of Fishes) recognises the following families:-
CARCHARIIDAE, chiefly from tropical seas. The Blue Shark (C. glaucus) and the White Shark (C. vulgaris) attain a length of from 12 to 15 feet and 20 to 25 feet respectively. [DOGFISH, HAMMERHEAD.]
LAMNlDAE, containing large pelagic forms. To this family belongs the Man-eating Shark (Carcharodon rondeletii), which has been known to attain a length of 40 feet. The Challenger Expedition obtained from the ooze teeth similar to but twice as large as those of this species, so that the larger form must have become extinct within rccent times. [BASKING SHARK, FOX-SHARK, PORBEAGLE]
NOTIDANAE, from tropical and subtropical seas. About 15 feet seems to be the greatest length.
CESTRACIONTIDAE.- There are four species of a single genus (Cestracion). None exceeds 5 feet in length. The teeth are broad and pad-like.
SPINACIDAE.- Here belong the Spiny Dogfishes [DOGFISH], and the Greenland Shark (Loemargus borealis), which grows to a length of about 15 feet, and is a persistent foe of the whale. The Spiny Shark (Echinorhinus spinosus), a Mediterranean ground shark, has the skin covered with spiny tubercles.
PRISTIOPHORIDAE,- This family contains forms like small sawfishes, but with lateral gill slits, and two long tentacles at the base of the saw.