Differs from Diadema in ambulacral tuberculation. In Diadema there is only a single primary ambulacral tubercle to each compound plate whereas in Echinothrix the primary tubercle is joined by four to six other tubercles only a little smaller, and the perradial tuberculate band thus appears broad and densely tuberculate.
Echinothrix diadema can be distinguished from the type species by: ambulacra not raised aborally, no naked median area in the interambulacra; periproct not largely swollen, with no white platelets present in the membrane.
Ambulacral spines of E. diadema similar to the type species, however, interambulacral spines are distinct in that they are non- verticillate, having longitudinal ridges, with spines distinctly flaring distally in adults.
This genus has been reviewed by Coppard & Campbell (2006a, b).
Coppard, S. E. & Campbell, A. C. 2006a. Taxonomic significance of test morphology in the echinoid genera Diadema Gray, 1825 and Echinothrix Peters, 1853 (Echinodermata). Zoosystema 28, 93-112.
Coppard, S. E. & Campbell, A. C. 2006b. Systematic significance of trident pedicellariae in the echinoid genera Diadema and Echinothrix. Invertebrate Biology 125, 363-378.
Mortensen, T. 1940. A monograph of the Echinoidea. Volume III. 1, Aulodonta. C.A. Reitzel, Copenhagen.
Peters, W. 1853. Monatsber. Akad. Berlin 1853, p. 487.