ABSTRACT
Marine organisms have developed a wide range of mechanisms allowing them to attach to or manipulate a substratum. The phylum Echinodermata is quite exceptional in that all its species, whatever their life style, use attachment mechanisms. These mechanisms allow some of them to move, others to feed, and others to burrow in particulate substrata. In echinoderms, adhesivity is usually the function of specialized structures, the podia or tube-feet. Based on their external morphology only, echinoderm podia can be divided into six broad types: disc-ending, penicillate, knob-ending, lamellate, ramified, and digitate. Most podia of regular echinoids, asteroids (except members of the order Paxillosida), and dendrochirote and aspidochirote holothuroids end with a disc. They are involved in locomotion and attachment, the disc being the site of contact with the substratum. In diadematoid and arbacioid echinoids, aboral podia are knob-ending and involved mainly in respiration.
