| Blastoids |
 |
| Crinoids |
 |
| Starfish |
 |
| Sea Urchins |
 |
Ancient Species
Echinoderms
Echinoderms are animals with hard plates or spines in their skins (rather than on top of them). The plates are made of calcite which is the principal mineral in limestone.
There are two groups of echinoderms: those with stalks and those without them. Echinoderms with stalks include blastoids and crinoids. Those without stalks include starfish and sea urchins.
Echinoderms include: