The whale shark (Rhincodon typus) is the largest fish in the world; with its vast size it resembles the whales from which its common name is derived. The head is flattened and the wide mouth, positioned at the tip of the snout, stretches almost as wide as the body. The dorsal fin is particularly large and the tail has a half-moon shape. The patterning of the body is very distinctive with its dark greyish-blue colour on the back and sides, and array of pale yellow blotches; the undersurface is pale. Stout ridges travel the length of the body, ending at the tail shaft. Five massive gill slits occur on the side of the head and within these there is a sieve like structure of cartilage. Curiously, the mouth contains around 300 tiny teeth although the function of these is unknown. Whale sharks have been tracked travelling for thousands of kilometres.