pelmetazoa; they are sessile <attached to substratum by long stalk (sea lilies) and some are free swimming (feather stars).mouth and anus are present on the upper surface (oral surface). madreporite is absent.ambulacral grooves are open. class crinoidea: this class includes the oldest and most primitive form.some are stalk less and free moving.viscera is enclosed in a calcareous test called theca .arms are biramous and bear pinnules and help in food capture. tube feet do not bear suckers. some attach to the substratum by cirri. eg: ptilocrinus,bathycrinus and neometra.