Tube feet are the many small tubular projections found most famously on the oral face of a sea star's arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand dollars and sea cucumbers and many other sea creatures.
Tube feet function in locomotion, feeding and respiration. The tube feet in a sea star are arranged in grooves along the arms. They operate through hydraulic pressure. They are used to pass food to the oral mouth at the center, and can attach to surfaces. A sea star that is overturned simply turns one arm over and attaches it to a solid surface, and levers itself the right way up.
Tube feet allow these different types of animals to stick to the ocean floor and move very slowly.
Tube feet consist of two parts: ampulla and podia. Ampulla contain both circular muscles and longitudinal muscle, whereas the podia contain the latter only. Thus the podia use suction to attach to the substratum.
Famous quotes containing the words tube and/or feet:
“One of the great natural phenomena is the way in which a tube of toothpaste suddenly empties itself when it hears that you are planning a trip, so that when you come to pack it is just a twisted shell of its former self, with not even a cubic millimeter left to be squeezed out.”
—Robert Benchley (1889–1945)
“There is, however, this consolation to the most way-worn traveler, upon the dustiest road, that the path his feet describe is so perfectly symbolical of human life,—now climbing the hills, now descending into the vales. From the summits he beholds the heavens and the horizon, from the vales he looks up to the heights again. He is treading his old lessons still, and though he may be very weary and travel-worn, it is yet sincere experience.”
—Henry David Thoreau (1817–1862)