A small and distinctive order of valvatacean Asteroidea with long, straight-sided arms and relatively small disks. The skeleton is differentiated into marginals, actinals, and abactinals, and there is a clear calycinal ring. Both supra- and inframarginals are present and are offset or alternate rather than vertically aligned as they are in other asteroids. Intermarginal ossicles are not present. On the oral surface the longest actinal row lies adjacent to the ambulacral groove. Digestive and reproductive organs are confined to the disc and most proximal parts of the arms and do not extend well into the arms as in other valvataceans. Dorsal longitudinal muscle bands lie free within the arms and are anchored into the body wall only at their distal and proximal ends.