The Echinoid Directory

Major skeletal test characters supporting cladogram [extant taxa in bold]:

1. Perradial ridge developed on basicoronal plates; internal partitioning of adradial bars and stellate ambulacral partitions.
2. Long primary perradial food groove trunk that trifurcates or splays irregularly distally.
3. Food groove bifurcates.
4. Food groove curves outwards, with secondary branchlets arising from inner side.
5. Food grooves bifurcates twice to give rise to a channel up the centre of each column of plates (water vascular system expands over interambulacral zones). Food groove beyond primary trunk a true groove rather than a raised band of dense pores.
6. Five gonopores.
7. Food groove bifurcates at distal end of basicoronal circlet.
8. Periproct midway between margin and peristome, opening in first pair of post-basicoronal interambulacral plates.
9. Interambulacra disjunct on oral surface, but first post-basicoronal ambulacral plates not significantly enlarged.
10. Food grooves extending onto aboral surface around posterior part of test.
11. Test thin margined; weak posterior notch and posterior ambulacral notches; internal buttressing very dense and forming honeycomb-mesh
12. Interambulacra disjunct on oral surface, with enlarged second ambulacral plates
13. Tubercles on oral surface differentiated into locomotory areas and food-gathering areas (corresponding to spine functional differentiation); accessory pores absent (or extremely sparse) on aboral surface; periproct opening within first post-basicoronal interambulacral plates.
14. Ambulacral lunules or notches of the cross-linked type; primary food groove devoid of large pores.
15. Periproct facing into deep anal notch or lunule.
16. Anal lunule fully formed.
17. Ambulacral notches or lunules of the festooned type; interambulacral zones as wide as ambulacral zones at the ambitus