Differs from other echinothurioids in having a continuous adradial series of demiplates aborally, with the large element completely occluded from the adradial suture. The lack of a hyaline hoof at the end of oral spines distinguishes this taxon from Echinothuriidae, while the lack of large adoral tubercles with sunken areoles and sphaeridia on just one of the two accessory plates in each triad distinguish it from the Phormosomatidae. Mortensen (1935) placed this taxon in the Phormosomatidae on the basis that it lacked spines with a hyaline hoof, but this is a plesiomorphic feature. It is probably sister group to the Echinothuriidae.
Mortensen, T. 1935. A monograph of the Echinoidea. Volume 2, Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C.A. Reitzel, Copenhagen.