There are perhaps no other animals on earth as feared or as misunderstood as the sharks. Books and movies have given the impression that the world's oceans are teeming with hungry sharks waiting to attack and devour any swimmer who dares enter the water.
Most people imagine a shark to be a large, gray, torpedo-shaped animal.
Neither view gives the full picture. Sharks and their relatives, the skates and stingrays, are very different from other fish because they have skeletons made of cartilage , a tough, flexible material that also supports the ears and noses of human beings. There are other differences between these elasmobranchs , or cartilaginous fish, and bony fish. Bony fish have a hard covering on their gill slits, but on sharks the five to seven gill slits are clearly visible. Instead of smooth, slimy skin with bony scales, sharks have rough skin made up of tiny teeth-like structures called dermal denticles .