Isorophida
Isorophida is an extinct order of prehistoric echinoderms in the class Edrioasteroidea. Isorophids are characterized by a disc-shaped, dome-shaped or club-shaped theca with ambulacra typically limited to the upward-facing oral surface which is bordered by an peripheral rim that flares outward parallel to the substrate. The aboral surface is unplated.
Isorophids are the most common order of edrioasteroids.