Whale sharks have a mouth that can be 1. 5 m (4. 9 ft) wide, containing over 300 rows of tiny teeth and 20 filter pads which it uses to filter feed. Unlike many other sharks, whale sharks' mouths are located at the front of the head rather than on the underside of the head. Whale sharks have five large pairs of gills. The head is wide and flat with two small eyes at the front corners. Whale sharks are dark grey with a white belly. Their skin is marked with pale grey or white spots and stripes which are unique to each individual. The whale shark has three prominent ridges along its sides, which start above and behind the head and end at the caudal peduncle. Its skin can be up to 15 cm thick and is very hard and rough to the touch. The shark has two dorsal fins set relatively far back on the body, a pair of pectoral fins, a pair of pelvic fins and a single medial anal fin. The tail has a larger upper lobe than the lower lobe (heterocercal). The whale shark's spiracles are just behind its eyes.