Hundreds of species of sharks—in every shape and size—swim the world's seas and rivers. Meet three of them.

Hammerhead Shark
With their bulky, T-shaped heads, hammerhead sharks are a strange sight. But their odd build is what keeps these skillful hunters ahead of their prey. Widely spaced nostrils give hammerheads an awesome sense of smell. And, some scientists believe, the "hammer" acts like a boat's rudder, helping the sharks turn quickly. With a tool like that, these sharks have no problem snagging stingrays and other fast-swimming fish.

Swell Shark
It's a fish-eat-fish world. In fact, only on a computer screen would a swell shark dare to come this close to a hammerhead. Swell sharks are hunted by bigger sharks. To get out of a jam, they get into one. Squeezing between two rocks, they swallow water so their belly blows up like a balloon. Once they're stuck, no one moves 'em. At night, swell sharks do a little hunting of their own. They glide along the ocean floor, snacking on sleeping fish. What a nightmare!

Nurse Shark
Unlike many sharks, nurse sharks don't need to keep swimming in order to breathe. They spend most of their time in shallow waters. These slow, awkward swimmers often use their fins to crawl along the ocean floor. With the barbels (feelers) at the corners of their mouths, they feel for crabs, shrimp, and clams in the sand. Then, with a powerful sucking motion, they vacuum up their prey. They can even suck snails right out of their shells!