A black urchin with very long thin spines, in crevices by day and out on rock at night.
To about 8 cm across the test, with black spines several times that length, very thin and brittle. It is the eastern Pacific member of the same genus as the Caribbean and Indo-Pacific long-spined urchins and looks like them: an almost black animal that is mostly spines.
By day it wedges into crevices and under ledges, often several together; at night it moves out onto open rock to graze. It is one of the main grazers and rock-eroders in the eastern Pacific and where it becomes abundant it removes enough coral and rock to change the ground. The spines break off in skin at a touch and are difficult to remove, and they will go through a thin wetsuit and through a glove. They carry no venom, so the injury is a mechanical one: painful, slow to settle, and prone to infection if fragments are left. The practical point is that it sits in exactly the holes and ledges a diver reaches into for a handhold in surge.
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.