subanal fasciole present (secondarily lost in some); crosses interambulacral plates 4a, 4b in the posterior interambulacrum
sternal plates paired and symmetric; rear of sternal plate abuts ambulacral plate 5.
Lower Cretaceous (Albian) to Recent; worldwide.
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: