Short blunt spines like pegs, usually encrusted with algae, wedged under rubble by day.
Test diameter is not given in any source consulted; the figure usually quoted is the overall width including spines. Thick blunt brown to rust-coloured primary spines, usually encrusted, with a five-part rosette on the upper surface.
Against the rock-boring urchin the separation is spine thickness: club-like here, slender and pointed there.
About six to sixty metres in rubble, seagrass and reef, wedged into crevices by day and feeding at night on coral and sponge.
Like the rock-boring urchin, it did not take over the grazing lost in the long-spined urchin die-offs.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.