One of the numerous external, fluid-filled muscular tubes of echinoderms, such as the starfish or sea urchin, serving as organs of locomotion, food handling, and respiration[BTO]. 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[WP]. [ http://purl.obolibrary.org/obo/BTO_0001919 http://en.wikipedia.org/wiki/Tube_feet ]