The largest shark is the whale shark. The whale shark grows up to 60 feet in length and can weigh up to 20 tons. The smallest shark is the dwarf shark. It is less than 6 inches long. Most sharks are six to seven feet long.
Most sharks are gray and have a leathery skin.
The bones of the shark are soft and made of cartilage. Their bodies are covered with small tooth-like spikes called denticles instead of scales. A shark must keep moving to keep afloat. Other fish have balloon-like sacks inside them called swim bladders which fill with air or gas to keep them afloat. Sharks do not have swim bladders.