| Marine invertebrates include ammonites, echinoderms, bivalves and crustaceans, but infaunal elements are rare. |
| Others have maintained that the earliest brachiate echinoderms had only three arms. |
| The calcitic ossicles of crinoids, as is typical of echinoderms, form an internal skeleton that provides support and protection. |
| Ophiuroids are a large group of echinoderms that includes the brittle stars and basket stars. |
| Most radially symmetric animals are sessile, however, echinoderms are able to move. |
| The beach sands are dominated by shells of bivalve mollusks, mainly venerids, gastropods, and echinoderms. |
