Purple Short Spine Urchin (Echinometra sp.)

Echinometra's claim to fame is architectural: it grinds a shelter pit directly into reef rock using its own spines and test, wearing the same burrow down over years until the urchin is essentially potted in solid stone. Those spines are short, thick, and deep purple rather than the long needle spines of a pincushion or longspine urchin, which makes it a lower-risk urchin to reach past during tank maintenance. It grazes algae from rock and glass steadily, day or night, and rarely bothers anything else in the tank.

Care level: Easy · Temperament: Peaceful · Max size: ~2" body · Min tank: 20 gal · Reef safe: With caution (may knock over frags) · Diet: Herbivore, algae