Crinoids or "Sea Liilies" are marine animals, living in shallow waters and in depths as great as 6,000 metres. The name derives from the Greek word krinon (meaning "lily") and eidos (meaning "form"). This fossil was formed in the Silurian period. As the Ordovician ice age ended, the sea-levels rose and the period became one of extensive seas and maritime reefs. It was at this time that bony fish first made their appearance.