Posted by: lauraearly | February 16, 2011

Thousands of tube feet on our fingertips

Students Oliver, Kathryn, Nick, and Max count sea stars at low tide.

Yesterday, we set out with four future scientists in search of some echinoderms. “Echinoderm” comes from Greek words meaning spiny skin, and  sea stars, sand dollars, and sea urchins are all part of this phylum.

At low tide, we scoured the  sandy bottom of the shallows for these spiny skinned invertebrates, and we were lucky enough to find more than a few. We counted over 20 sea stars!

Oliver holds a sea star.

As we held the sea stars and felt their rough skin, we realized how they got their name “echinoderm,” but on the underside of the sea star we got to feel something equally as neat.

Sea stars have hundreds of little projections called tube feet. These feet are quite different from our own, and are actually part of the sea star’s water vascular system which it uses to pump seawater through its body. The tube feet are the ends of these vessels where the seawater exits the sea star.

Tube feet are useful to the sea star in many other ways, too. They help the creature move from one place to another, sense what is going on around them, bury themselves in the sand, and move food to their mouth. Tube feet can also act like suction cups to help sea stars cling to rocks or other structures under the water. Check out these feet in action in the video clip below:

With hundreds of tube feet on each sea star and over 20 sea stars, we encountered a lot of multitasking feet!

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