Echinocyamus pusillus is a small sea urchin with an oval, flattened body measuring up to 15 mm long. The calcite skeleton is completely covered with fine short spines and coloured grey to greenish. Specimens become completely green when injured, a characteristic the species shares with some other sea urchin species.
Degraer, S.; Wittoeck, J.; Appeltans, W.; Cooreman, K.; Deprez, T.; Hillewaert, H.; Hostens, K.; Mees, J.; Vanden Berghe, E.; Vincx, M. (2006). The macrobenthos atlas of the Belgian part of the North Sea. Belgian Science Policy. D/2005/1191/3. ISBN 90-810081-6-1. 164 pp. (look up in IMIS)