GENERAL HISTOLOGY

Detailed explanation-1: -Sea urchins roll themselves over by a concerted action of their tube feet and spines.

Detailed explanation-2: -Some groups of echinoderms, such as sea urchins (Figure below), have spines that protect the organism. Sea cucumbers use these spines to help them move. Another echinoderm, a sea urchin (Echinus esculentus), showing its spines. Echinoderms have a unique water vascular system.

Detailed explanation-3: -An echinoderm moves by using many tube feet. Tube feet are small, delicate projections attached along the side of a water-filled tube called a radial canal. Figure 3.85 shows some examples of echinoderm tube feet. Tube feet extend through the small holes in the skeleton to the outside.

Detailed explanation-4: -The tube feet are part of the urchins water vascular system. They work like a hydraulic system. The urchin contracts its muscles to push water into the tube feet. This extends the feet outwards.