The Echinoid Directory

Characters supporting cladogram:-
1. More than one pore and tube-foot associated with each ambulacral plate outside petals.
2. Sphaeridia enclosed within ambulacral plates, not in open pits. Ambulacral pores and tube-feet along horizontal sutures and/or lie scattered in bands within plate not simply forming a vertical adradial band.
3. Petals composed of alternating primary and demi-plates. Interambulacral zones always disjunct adorally.
4. Perignathic girdle composed of five interradial muscle-attachment pegs.
5. Interambulacral zones terminate adapically in one or more single plates.