whale shark, large, plankton-eating shark, Rhincodon typus, found in all tropical seas of the world. The largest known specimens are 50 ft (15 m) long, making them the largest fish in the world. The whale shark feeds largely on plankton, as well as on small fish and crustaceans. It is the only large shark with its mouth at the front of its head rather than on the underside. The mouth is equipped with many rows of tiny teeth, and the throat has numerous long slender structures called gill rakers, which form a fine mesh for straining food from the water. The whale shark's body is stout but streamlined, like that of a whale. It is dark brown above, with many white or yellow spots, and white or yellow below. The whale shark is a docile, torpid fish; it does not attack, even on provocation, but has been known to collide with boats. It is classified in the phylum Chordata, subphylum Vertebrata, class Chondrichthyes, order Selachii, family Rhincodontidae.