[2] They most likely form a paraphyletic grade along sea cucumber stem lineage,[3] although some sources still consider the question of ophiocistioid monophyly unresolved.

[4] Ophiocistioidea is named from the Greek words "ophis" (snake) and "kiste" (box).

[5] Ophiocistioids had a flattened globular body encased in a solid test of calcareous plates, similar to that of a modern sea urchin.

Five ambulacra radiated outwards from the mouth across the lower surface, but only continued around the edge to just under the level of the anus.

[6] Ophiocistioids had unusually long tube feet emerging from near the mouth and around the edges of the body.