eocrinoid

The term "eocrinoid" refers to an extinct class of echinoderms that existed from the Lower Cambrian to the Silurian periods, approximately 570 to 430 million years ago. Eocrinoids were typically stalked, with their soft parts enclosed in a chamber called a theca. This theca gave rise to feeding appendages known as brachioles.1

Echinoderms, the phylum to which eocrinoids belong, are marine invertebrates characterized by a skeleton made of calcium carbonate and, in most fossil and living representatives, five-part body symmetry (pentamerous). They also possess a unique water-vascular system. The fossil record of echinoderms is extensive, though many questions remain about their early evolution. Scientists speculate that early echinoderms may have lacked calcite skeletons, which is why Precambrian fossils are scarce.12