Within the echinoderm's body, a tiny bulb attached to the tube foot forces water into it to make it lengthen. An internal system of water-filled canals connects the tube feet to each other and to a sievelike plate that usually opens to the sea water. The entire system of tube feet and canals is called the water vascular system. Echinoderms reproduce by laying eggs that develop into larvae and swim freely. The larvae sink to the ocean bottom and change into the adult, radial form.
Echinoderms make up the echinoderm phylum, Echinodermata.
John C. Ferguson, Ph.D., Professor of Biology and Marine Science, Eckerd College. How to cite this article.