Crinoids are an ancient fossil group that first appeared in the seas of the Middle Cambrian, about 300 million years before dinosaurs. They flourished in the Palaeozoic and Mesozoic, and some survive to the present day. Although sometimes different in appearance from their fossil ancestors, living forms provide clues about how fossil crinoids must have lived.
Crinoids are marine animals belonging to the phylum Echinodermata and the class Crinoidea. An array of branching arms (brachials) is arranged around the top of a globe-shaped, cup-like structure (calyx) containing the main body of the animal. In many fossil forms the calyx was attached to a flexible stem that was anchored to the sea bed.