Many people think that all sharks are ferocious, dangerous animals. Of the 380 species of sharks, only a few kinds have been known to attack humans.
Most sharks have their mouths on the underside of the head.
The mouth has rows of sharp teeth that are replaced as they wear out. Sharks vary greatly in size and habit. Whale sharks are the largest of all fish and can grow up to 12 m long and weigh up to 14 tons. The smallest sharks are the tiny pygmy sharks which are fully grown at 25 cm long. Sharks have a skeleton made up of a tough, elastic substance called cartilage.