Today, to the untrained eye, that common origin isn't obvious, because most sharks and rays look so different from one another. Some sharks are reputed to be able to detect minute quantities of substances such as blood in water from several hundred feet away. Some sharks grow to be only a foot long. Despite its size, the Whale shark feeds on some of the ocean's smallest life, the tiny plants and crustaceans that drift near the surface. In fact, fewer than 50 shark species grow to be longer than six feet, and most rarely reach three feet long.
Sharks also vary in lifestyle.
Sleek Mako sharks, for instance, may spend their days cruising the seas at up to 40 miles per hour, hunting fish and occasionally launching themselves into the air with acrobatic leaps. Angelsharks, however, prefer a more sedate existence. They bury their camouflaged, flat bodies in the sandy sea bottom and wait for unsuspecting crabs to scuttle by. Most sharks, however, have to keep moving to breathe and stay alive. That's because they breathe by swimming forward with their mouths open, allowing oxygen-filled water to sweep across their gills.