Crinoids are marine echinoderms (phylum Echinodermata). The name comes from the Greek word krinon, which means ‘a lily’, and the Chinese name ‘sea lilies’ comes from its appearance. It is not a plant but rather an echinoderm. A complete crinoid fossil comprises three parts: a crown, a stem and roots. The crown, which is composed of the calyx and the wrist (arms), looks like the calyx and petals of a flower. The calyx is the main part of a crinoid and is composed of calcium carbonate plates. The calyx is crucial for identifying crinoids. It is often globular or cup-shaped with a few overlapping calcareous plates. Because crinoids are marine animals, they first appeared in the Ordovician, flourished in the Silurian and reached their peak in the Carboniferous.