A group of small, deep-water cassiduloid echinoids with neotenous characteristics, treated as an order by some workers; possibly polyphyletic. The presence of bourrelets and phyllodes, the elongate first ambulacral plates, the undifferentiated tuberculation, and undifferentiated posterior interambulacral plating all indicate their relationships lie with cassiduloids. The only character shared by members of this group is the lack of petals (they have simple ambulacral pores only). Other characteristics, such as apical disc plating, are varied, indicating at least two independent origins from shallow-water cassiduloids.