1. 28-4 Echinoderms

2. endoskeleton Structural support located inside the body of an animal.

3. Water Vascular System System of internal tubes in echinoderms that carries out essential functions such as feeding, respiration, circulation, and movement.

4. Madreporite sievelike structure through which the water vascular system of an echinoderm opens to the outside.

5. Tube foot Suction-cuplike structure attached to radial canals of echinoderms; used to walk and to open shells

6. Key Concept Echinoderms are characterized by spiny skin, an internal skeleton, a water vascular system, and suction-cuplike structures called tube feet. Most adult echinoderms exhibit five-part radial symmetry.

7. Key Concept The water vascular system, which is filled with fluid, carries out many essential body functions in echinoderms, including respiration, circulation, and movement.

8. Key Concept Classes of echinoderms include sea urchins and san dollars; brittle stars; sea cucumbers; sea stars; sea lilies and feather stars.