SEA LIFE - Sharks - In all the oceans of the world there are approximately 375 species of sharks.. The shark is one of the oldest living creatures in the sea and is virtually unchanged since prehistoric times. They have inhabited the earth for over 400 million years. They all belong to the Chrondrichthyes class because they have skeletons made of gristle like cartilage. They range in size from less than one foot (dog shark) to 60 feet and more than 17 tons like the giant whale shark. They mostly live in tropical to temperate waters. There have been some shark's found in the Antarctica. The Great White is now not allowed to be fished for food or sport as it is becoming endangered. One of the unusual features of most sharks are their many rows of teeth. They have seven rows of sets of teeth. These extra sets of teeth move up in place within 24 hours with the loss of a tooth. So their teeth are like rippers and the jaw so powerful that he tears off meat with little effort in an instant. Only a few shark's are responsible for attacks to humans despite their reputation. Sharks do not dwell usually on the reefs but only visit occasionally for food. If divers and swimmers do not kill fish the danger in minimal. Surfers pose a sight threat as they have been mistaken for sea lions on the West Coast. Several sharks are still fished for food commercially. In Japan is is a delicacy and very expensive.