Starfish or sea stars are carnivores that eat clams, mussels, oysters, arthropods, sea urchins and even small fish. Some species also eat some sponges, bryozoans, coral polyps.
Sea stars have two separate stomachs: the cardiac stomach and the pyloric stomach. The cardiac stomach can be pushed out of the body through the mouth to engulf and digest food. Digestive juices liquify the animals tissues and this, together with the stomach are sucked back into the sea star.
Sea stars are also thought to use their tube feet to pass small particles of food along to the mouth and they can even absorb nutrients from organic material already dissolved in the sea water.
The underside of a starfish or sea star is covered with hundreds of tube feet which it uses for walking around, attaching to rocks and other hard surfaces, and for collecting food.
Sea stars use a water vascular system to lift and swing forward a tube foot, and then plant it on the ground and push backwards. Suction caps on the end of each tube foot enables the sea star to walk on uneven and sloped surfaces, as well as hang onto sheer surfaces.
Water enters the system through the madreporite, (a pore or opening that filters particles out of the water) and travels via radial canals tot he top of the tube feet . The water is then squeezed into the foot, causing it to extend.
Varying the water pressure enables the sea star to extend and retract the tube feet. Each tube foot can be withdrawn using its attached muscles.
The feet latch onto a surface and then move in a wave, with one body section attaching to a surface as another one releases. The sea star moves in a particular direction by gripping with some of its tube feet and pulling itself along.
Website created by Jenny Stevenson - June 2006.