Crinoids are marine animals that make up the class Crinoidea of the echinoderms. Crinoidea comes from Greek ‘krinon’ meaning “a lily” and ‘eidos’ ~ “form”.
Strictly speaking ~ ‘sea lily’ refers to crinoids which in their adult form are ‘attached’ to the sea bottom by a stalk. ‘Feather-stars’ refer to the ‘unstalked’ free-moving form. The earliest known group of ‘sealilies’ date back to the Ordovician period ~ some 443 million years ago.
Through abrupt adaptive radiation and a selective mass extinction ~ Triassic radiation resulted in forms ‘possessing flexible’ arms to become widespread ~ motility in response to fleeing predators also became more prevalent.
These changes demonstrate how well the echinoderms have adapted to continue their filter-feeding strategy.