Crinoids are not very familiar organisms today, mainly because they tend to inhabit deeper waters and are therefore difficult for the average person to observe. However, modern forms, probably like their ancestors, are colourful and bright, giving them their common name, the sea lillies.
Only one family survived the end-Permian extinction event, the Articulata. The articulates are a monophyletic subclass belonging to the Cladida and they form the crown-group.
Over 250 articulate genera are known, although there may be many more. Their position in the deeper parts of the ocean makes study relatively difficult and there are likely to be some undiscovered species. Nearly two-thirds of articulate genera are extant.