Short blunt spines like pegs, wedged under Galapagos rubble by day and grazing at night.
Test diameter is not given in any source consulted. Thick, blunt, cylindrical primary spines, usually so encrusted that the animal is hard to see: about nine in ten individuals carry other organisms, with over twenty species recorded on a single urchin.
It was separated from the Pacific slate pencil urchin on genetics and the two cannot be told apart underwater, so geography is the practical answer.
Shallow rocky reef where there are crevices to wedge into. It grazes coral and algae, and at high density it strips reef to barren rock and holds back Pocillopora recovery. The removal of lobsters and predatory fish is implicated in how abundant it has become.
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.