Rock-boring Urchin

About

The rock-boring urchin (Echinometra mathaei) is one of the most widespread sea urchins on Indo-Pacific and Red Sea reefs, and its name tells you exactly what it does. Using its teeth and spines, this urchin slowly grinds depressions into hard substrate, eventually creating a snug pit it settles into permanently. That behavior makes it a fascinating animal to watch, though it also means you need to be thoughtful about what rockwork you put in a tank with one. In the wild, you find these urchins packed into surge zones and shallow reef flats, often in dense aggregations where every individual has its own custom-carved hollow. Coloration varies quite a bit across its range, from reddish-brown to near-black, with spines that are relatively short and stout compared to many other urchins. For a saltwater invert, it is considered a forgiving choice, tolerating the kinds of water quality fluctuations that beginners sometimes encounter. It will graze on algae growing over rock surfaces, which makes it genuinely useful in a tank dealing with nuisance algae growth. Just be aware of its excavating habits and give it appropriate companions and hardscape.