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Jaws open, a tiger shark springs forward. It sinks its razor-sharp teeth into a giant manta ray's fin. The ray rears up. A red cloud of blood oozes from it.

With the taste of blood in its mouth, the shark lunges forward again. It misses as the ray twists out of reach and speeds away.

Bleeding, the ray begins a long journey. It swims along the coast of Africa, looking for food and help.

Two days later, it swims into a coral reef. It heads to the top of the reef where it settles down, resting. Spotting the ray, small groups of fish swim out of their hiding places. They circle, then swarm around the ray. This is the help the ray has been looking for. They're "cleaner fish."

The cleaner fish go to work. One kind eats parasites clinging to the ray's belly. Another kind eats algae that have built up around the ray's mouth. A third kind cleans out the ray's bite wound.

After a few hours, the fish are done and the ray is ready to move on. It swims away from the reef, back into deeper water.

The cleaner fish and the ray help each other. The fish get a good meal and the ray gets clean. This is an example of mutualism. Mutualism happens when two living things need each other.

Mantas are only one kind of ray. More than 500 ray species swim in the ocean. Rays are fish, closely related to sharks.

Think of a ray as a flat shark, minus the sharp teeth. Some kinds have a body shaped like an oval. Others have a body shaped like a diamond. Then there's the guitar ray. It really is shaped like a guitar.

Different rays grow to different sizes. Some could sit in the palm of your hand. Others are larger than four cars parked side by side. The short-nose electric ray is the size of a pancake. The manta is much larger. It weighs as much as an elephant.

No matter its shape or size, all rays have a tail and fins on theirs sides. These fins are called pectoral fins. They almost look like wings. The cownose ray flaps its pectoral fins up and down like a bird. It is in constant motion. It dips and climbs, rarely resting on the seafloor.

Another kind of ray swims along the seafloor. It's the spotted stingaree. Its fins ripple from front to back. This motion pushes the ray forward. It also lets the ray hover over prey.

A ray uses its fins and tail together to help it move through the ocean. During a fight, a tail can also be a weapon.

Take the blue-spotted stingray, for example. It has sharp barbs on its tail. Each barb holds poison. In a fight, the stingray cracks its tail like a whip. It stings its attacker.

A ray has to be careful. It doesn't have a hard shell to protect itself. It doesn't even have bones. Instead, it has a skeleton made of cartilage. Cartilage is tough and it stretches a little. Still, it's not as strong as bone.

To see what cartilage is like, wiggle your nose with your fingers. Cartilage forms the tip of your nose.

Like all living things, rays are part of a food chain. They have to look for food and keep from becoming food. That's why rays have to look out for hungry predators, such as sharks.

A ray's eyes are on top of its body. It scans the water above looking for carnivores diving down to eat it.

Rays are carnivores, too. Their mouths are full of teeth the size of pinheads. Rows of these tiny teeth crush and grind prey.

A ray uses several senses to find food. It uses its senses of touch and smell. It also uses a sense humans don't have. It can sense electric signals from other animals. Together, these senses help rays hunt prey.

Take the Australian butterfly ray. As it swims, it gently stirs the sandy seafloor. Sometimes the shifting sands uncover a small fish or snail hiding in the sand. The ray then scoops up a meal.

The spotted eagle ray plows the ocean floor with its snout and fins. As it moves along, it digs up oysters, clams, and snails. The ray quickly snaps them up.

Both the spotted eagle ray and the Australian butterfly ray are bottom feeders. They find their prey on the seafloor.

Not all rays are bottom feeders. Some, like the manta, are filter feeders. Mantas eat plankton. These are microscopic plants and animals. When a manta comes upon plankton, it swims toward them. As it gets closer, the manta starts to roll. It flips over, end over end, amid the plankton.

As it spins, the manta uses flaps on the side of its head to scoop plankton and water toward its mouth. The manta then filters the water through its gills. The water gushes out. The plankton stays in.

Some rays have unique ways to hunt. A torpedo ray is a slow swimmer. Yet it has a special ability. It electrocutes its prey. Gliding above a fish, the ray stuns it with a jolt of electricity. The ray then gobbles up its shocked prey.

A sawfish has a flat, sword-like blade with teeth along both edges. A sawfish can use its saw as a shovel. It swims along the ocean floor, digging up food.

It also uses its saw to slash prey. It swims into a school of fish, shaking its head from side to side. As it swims, it slashes nearby fish. It then eats the pieces that fall to the ocean floor.

Rays live in many ocean habitats. They swim from the deep ocean to shallow coral reefs. Yet scientists still don't know much about them.

For example, they don't know how long rays live. They don't know if rays sleep or, if they do, for how long. They don't even know how important they are to a reef habitat.

Scientists also don't know why mantas sometimes breach, or jump out of the water. One theory says mantas breach to shake off parasites. Breaching also could be one way mantas communicate with each other.

When a manta splashes back into the water, it makes sound waves. The waves travel a long way through water. Other mantas might sense those waves. So a manta may be "speaking" when it's breaching.

For now, these and many other questions remain unanswered. Yet our knowledge of rays keeps growing. Scientists track and observe them. One day, they hope to have a more complete picture of rays and their role in their ocean habitat. For now, they study them one ray at a time.

Article by Gary Miller. Top-of-page image by James A. Dawson/Shutterstock. "Flat Sharks" appears in the May 2011 issue.