The great majority of members in this clade are readily distinguished from other spatangoids by their subanal fasciole. Those that have secondarily lost this fasciole can be identified because even in the absence of a subanal fasciole ambulacral plate 6 is geniculate and indents the posterior interambulacrum at the rear of the episternal plates.
The following genera are too poorly known to allow it to be placed in any family:
- Mauritanaster Lambert, 1920
- Cardiopatagus Pomel, 1883