1983, Ulrich Lehmann, Fossil Invertebrates, page 292,The enlarged rear interambulacrum on the oral side of holasteroids and spatangoids is known as the plastron.
2003, Gunther J. Eble, Developmental Morphospaces and Evolution, James P. Crutchfield, Peter Schuster (editors), Evolutionary Dynamics, page 47,Spatangoids constitute a monophyletic group of heart urchins that appears in the early Cretaceous (145 M.Y. ago) and ranges to the Recent.
2010, Kenichi Kanazawa, Adaptive evolution in Cenozoic spatangoid echinoids, Mike Reich, Joachim Reitner, Vanessa Roden, Ben Thuy (editors), Echinoderm Research 2010: 7th European Conference on Echinoderms, Göttingen, page 61,Oval tests with specific ventral morphology for efficient burrowing allowed spatangoids to burrow deeply in sand to avoid gastropod predation.
