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Green Sea Urchin Video Stock Footage
The tube feet of S. droebachiensis are actually composed of two parts: the ampulla and the podium. The ampulla is a hollow bulbous structure that raises the tube foot above the skeletal plates that surround the lateral canal. The podia extend off the ampulla and contain the muscular suckered structure used for attachment. The movement of the tube foot depends on the hydraulic pressure of the water vascular system, and individual muscle action. When the ampulla contracts, it forces the liquid into the podia which elongates. Once the podia has attached itself to the substrate, the longitudinal muscles of the podia constrict forcing that liquid back into the ampulla causing the podia to shrink and pulling the body in that direction, or food closer to the mouth. Tube feet that have been pulled off as the sea urchin is thrown around by the sea will quickly regenerate.
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