A short-spined urchin of seagrass beds that covers itself in shell, weed and debris, so it is often seen as a moving pile rather than an urchin.
Test five to eight centimetres. A greenish to purple test with short, often white-tipped spines, and almost always carrying shell, seagrass blades and rubble on its upper surface.
The other large Caribbean urchin has a dark test with dense uniform white spines and does not carry the same load of debris.
Nought to fifty metres, and common on seagrass and sand flats as well as on reef. The covering behaviour is what a diver notices. It is a heavy grazer of seagrass. The spines are short and harmless.
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.