How do starfish move

A. Using the hundreds of tube 'feet' that run beneath their arms. The starfish draws water through its body and feeds it through to these suctioned bottomed tubes, which are usually attached to rocks or prey.

This change in water pressure in its body causes contractions in the tubed feet allowing the starfish to move the tubed feet along a surface and so move around the ocean.

Q. Are starfish really fish

A. No, starfish, or sea stars as they're sometimes called, are actually echinoderms, members of the same group as sea urchins, sea cucumbers and sea lilies.

Echinoderm is Greek and means, rather aptly for starfish, 'hedgehog skin'. A starfish's skeleton is made up of numerous plates that move like flexible joints.

Q. Do all starfish have five points

A. No, when starfish are born they're symmetrical; the ones that have five points develop them as they grow. Some starfish end up with as many as ten arms, like the purple starfish that lives in the Gulf of Maine off the coast of North America.

This ability to grow arms doesn't just happen once; starfish can also grow back arms, even large parts of their body, if they loose them in an accident. As long as they've still got at least one arm and one fifth of their body they can become as good as new again, although it does take up to a year to return to their former selves.

Q. How big is the biggest starfish

A. Most species are no more than 20cm across, but one, Pycnopodia, can be as big as 1 metre in diameter.

Q. What do starfish eat and how

A. Most starfish are carnivores, feeding on shellfish, barnacles, sea snails, crabs and other starfish. Their mouths can be found on the underside of their body, but instead of eating their food internally they flip their stomachs out through their mouths and digest their prey on the outside. Once they've finished their stomachs are pulled back in until the next meal.

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by Lisa Cardy