; class Crinoidea, subclass Articulata)
An order of crinoids which lack a stem or column in the adult state and which swim freely. The uppermost ossicle of the column is modified into a conical or discoidal plate (a centrodorsal). This bears numerous cirri (see cirrus), which are used to grasp substrata. The order has existed since the Jurassic.
Subjects: Zoology and Animal Sciences.