The mysterious mollusk.

In the shallow coastal waters of North America, Hawaii, China, and the West Indies lurks an ocean dweller that has scared people for centuries. It's even been called a devilfish because of its frightening appearance.

Actually, though, this animal is more mysterious than scary.

What is it? It's an octopus.

Although some species grow to twenty-eight feet long, most are no larger than a grown-up's fist. They rarely attack people. And only a few, such as the blue-ringed Octopus of Australia, are poisonous.

8 Fascinating Facts About Octopi

1. The word octopus means eight feet.

2. An octopus swims by drawing water into its body and by squeezing it out through a funnel-shaped opening under its head. The direction of the opening, or siphon, controls the octopus' movement.

3. The siphon also provides protection. When an octopus is in danger, it can squirt black fluid from the opening. This fluid forms a dark cloud that allows the mollusk to escape from enemies.

4. Rows of round muscles on the tentacles act as suction cups. The octopus uses one arm to feel its way forward on the rocks. The other tentacles grab the rocky surface and pull the octopus along.

5. An octopus can change color to blend with its surroundings. Small bags of color, or pigment, are attached to its muscles and nervous system. When the octopus becomes excited, the pigment bags open. An octopus can become blue, gray, purple, brown, white, red, or even striped.

6. The octopus is a mollusk. It has a soft body, three hearts, no backbone and a tough called a mantle.

7. Living in underwater caves by day, the octopus comes out at night to hunt for crabs, clams, lobsters, and other shellfish, cracking open the shells with its tentacles and hard, parrot-beak jaws.

8. An octopus has eight tentacles (TEN-tuh-culs). If an octopus loses a tentacle, it can grow another one. This is called regeneration.

Illustrated by Martin Williams