- internal buttressing in the form of concentric walls around the periphery with or without more central pillars;
- a pair of sunken and enclosed sphaeridia in each ambulacrum;
- petals when well developed consisting of alternating primary plates and demiplates (N. B. apetalloid forms with simple ambulacral plating);
- perignathic girdle of 5 pairs of ambulacral elements (auricles);
- interambulacral plating on oral surface always disjunct.