Echinoderms are very rarely preseved in the fossil record because they are extremely fragile. However, in ideal conditions of rapid burial, spectacular specimens of sea urchins, starfish, and sand dollars can be found. Whole sea urchin tests (the exoskeleton or shell) are rare because they are made of plates that are weakly attached to each other. Sea urchin spines, however, are abundant in Miocene and Pliocene sediments.
M. J. O'Donnell