card
130

starfish

OLogy Series
animal
card
130

starfish

OLogy Series
animal

It's easy to see how the starfish got its name -- with their pointed arms, these creatures look like stars fallen to the ocean floor. But starfish aren't fish at all. Fish are vertebrates, animals with backbones. Starfish, like their close relatives sand dollars and sea lilies, are invertebrates, animals without backbones. It's no wonder scientists prefer to call them "sea stars."

The Starfish March
Starfish are certainly not the speediest creatures in the ocean, but they have a fascinating way of moving. A starfish "walks" along the ocean floor using water pressure and its tube feet, tiny tubes lining the bottom of each arm. At the tip of each tube is a small disk or sucker that works like a suction cup. To move, a starfish forces liquid into the tube feet, making them stiffen and reach out. When the suckers at the tips of the tube feet touch a hard surface, the starfish withdraws the liquid, creating a tiny vacuum. The suckers become powerful suction cups that hold the starfish to the surface. When the starfish is ready to move again, the tube feet contract and loosen their hold, pushing the starfish forward or backward a short distance. The starfish forces liquid back into the tube feet, and the process begins again. As you can guess, it's not a fast-moving pace — an average starfish moves about 10 yards per hour. How long does it take you to walk 10 yards?

If a starfish loses an arm, it will:

grow another arm in its place

never be able to move again

starve to death

Are you right?

Correct!

Sea stars have the ability to regenerate, which means if they lose an arm, another one will grow in its place. And if a sea star is cut in half, each half will become a new sea star.

A starfish has a stiff, inflexible outer skeleton.

Fact
or
Fiction
?

Fiction

A starfish has an inner skeleton covered with a thin layer of skin. The skeleton is flexible, so a starfish can move its arms to squeeze into tight spaces.

Starfish usually move in one direction.

Fact
or
Fiction
?

Fiction

Starfish don't have a front or a back, a left or a right. They can move in any direction.

starfish
Phylum: Echinodermata
Size: 4/5 inch to 4 feet (from tip to tip)
Habitat: every ocean of the world
Diet: clams, oysters, crabs, snails -- just about anything they can pull into their stomachs
Characteristics: typically have five arms, but may
have more; found in many colors
Significance: were living on Earth for more than a half a billion years before humans

Image credits: courtesy of Gerald and Buff Corsi, California Academy of Sciences.