Crinoids are sessile, filter-feeding benthic echinoderms restricted to marine environments. They are the sister group to the other echinoderms, which include sea cucumbers, sea stars, and sea urchins. Here is our current understanding of echinoderm evolution:
There are many scientists working to untangle the evolutionary relationships between echinoderms, a great place to follow the progress is the website created by the Echinoderm Tree of Life Project (EchinoTol) (http://echinotol.org/).
Modern crinoids are traditionally divided into those with and those without a stalk as adults.Stalked crinoids (Sea lilies) Stalked crinoids are currently restricted to depths greater than 100m. There are approximately 100 described species. Unstalked crinoids (Feather stars) Featherstars begin their lives as stalked crinoids, then detach to become mobile juveniles and adults. Many can crawl and some species are capable of swimming. Featherstars represent the majority of modern day crinoid diversity and are found throughout the world’s oceans. There are approximately 450 species described.