What is the common name of the group whose members are characterized by exoskeletons and a unique water vascular system? a. brachiopods b. medusas c. echinoderms d. tunicates

I believe it is Echinoderms cause that would include star fish which obviously have an exoskeleton for protection but they also have a pretty fancy water vascular system that is used for locomotion, feeding, respiration and excretion.