The relationships amongst the various genera are illustrated in the cladogram above. Characters supporting the various groupings are as follows:-
1. All ambulacral tubercles imperforate; interambulacral tubercles imperforate adorally, with or without rudimentary perforations adapically. Apical disc cap-like and forming an elevated platform at the apex of the corona. Suranal plate forming an integral part of the disc.
2. Sutural pitting developed on apical disc plates.
3. Small tubercles present in depressions along the sutures of apical disc plates
4. Ambulacral plating primitively bigeminate (may become unigeminate in some derived species); never trigeminate. Interambulacral tubercles always imperforate.
5. Periproct framed by three posterior genital plates and suranal plate only.
6. Periproct offset from the anterior-posterior axis towards posterior right ocular plate.
7. Ambulacral zones with distinct central band of granulation
8. Apical disc with ocular plates square-ended and protruding .
9. Inner columns of secondary ambulacral tubercles developed,