[3] It is generally black or blue-black in colour, and always dark (the spines show a blue sheen in the light).

It differs from Echinothrix calamaris in that the spines are not banded, except in juveniles, and that its anal sac is small and hardly visible, and the spines show a blue sheen (whereas dark morphs of E. calamaris show a greenish tinge).

Another similar species is Diadema setosum, which has longer spines and smaller test, the distinguishing feature being an orange ring around anal sac.

Females generally choose low-lying locations, presumably so the tiny larvae can have better protection from predators.

Saron marmoratus stays close for protection, like many fish of the families Apogonidae (cardinalfish) and Centriscidae (razorfish and relatives).