1. Sea urchins are echinoderms and shells are mollusks. Sea urchins walk on spines and tube feet on their bodies, which have tiny suction cups at the end that are able to grab onto any solid surface, and by extending and contracting these tiny tube feet, they can move quickly.

2, the shell's way of moving, such as scallops, sea moon shells, bell shells, etc. Their feet are reduced, the front closed-shell muscle has disappeared, but the back closed-shell muscle is developed and moved to the center of the body, through the back closed-shell muscle in the transverse muscle non-stop contraction, and make the two shells beat each other, resulting in the outer shell cavity of the rapid jet of water out of the body in the water to swim.