Sea urchins move by increasing or decreasing the amount of water in it's water vascular system thus allowing it to extend or contract its feet. The foot extension and contraction enables it to move about the water.
Sea urchins are spiny creatures that live in the sea. Because of the spines, they are often called the porcupine of the sea. Beneath the spines lies a hard outer shell known as the test. The test is made up of ten plates that surround the sea urchin. The sea urchin has tubular shaped feet that it extends through holes in every other panel of the test. The tubular feet are connected to the sea urchins' water vascular system. When the sea urchin wants to move it either pumps water in or out of the vascular system which allows it to control their feet movement.
It is recommended to be cautious of sea urchins while swimming in the ocean. The spines of some sea urchins contain poisonous toxins. When the sea urchin stings you the spine will break off and may end up splintered into the wound; this may result in painful burning or throbbing. The beauty of a sea urchin can be observed, but be very careful not to touch.