[Ebook] Encyclopedia of Aquarium & Pond Fish – Directory of Marine Invertebrates – Echinoderms
Starfish are the best-known echinoderms, but the group also features feather and brittle stars, as well as sea urchins and sea cucumbers. While they vary in shape, all these creatures have an internal body structure formed from calcium and tube feet that enable them to move over the seabed.