EVERYDAY SCIENCE

Detailed explanation-1: -Define Echinoderm. Invertebrates with an internal skeleton and a system of fluid-filled tubes called a water vascular system. Examples: sea cucumbers, sea starts, sea urchins, and sand dollars.

Detailed explanation-2: -Examples of echinoderms include sea stars, sea urchins, sea cucumbers, brittle stars, and feather stars (Fig. 3.83). Although they may appear very different, echinoderms all have two major defining characteristics that set them apart from all other animals: a water vascular system and five-sided radial symmetry.

Detailed explanation-3: -Echinoderms are characterized by a unique coelomic water vascular system. This is a hydraulically controlled system consisting of a circumoral ring around the esophogus with connecting radial canals each leading to an ambulacrum. The radial canals in crinoids run along each arm into an ambulcral groove and tube feet.