There are about 6,000 kinds of echinoderms. Starfish, brittle stars, sand dollars, sea urchins, and sea cucumbers are among the most common kinds.
All echinoderms have an internal bony skeleton.
Their spines are a part of the skeleton. Adult echinoderms have radial symmetry. Their body parts are arranged around the center of the animal like the spokes of a wheel around the hub. Echinoderm bodies are usually divided into five sections with the mouth in the center. Echinoderms are the only animals that have many tiny tubelike structures called tube feet.