Collector Urchin - Tripneustes gratilla

Collector Urchins (Tripneustes gratilla, also called "Sea Eggs") live up to their name, sweeping over substrate and reef and collecting bits of whatever they encounter to use as camouflage. This can include algae, polyps, shells, substrate, even the occasional snail. Their spines are often moving very quickly, and are held at strange, skewed angles that would indicate a health issue for many other urchins. Collector Urchins have short spines that are variable in color. Most are black and white but may have highlights of red or orange depending on their region.

Urchins are grazers that will roam about the tank searching for food and algae on the substrate and rockwork. Most will not actively eat corals, but some delicate corals may be damaged if the urchin crawls on top of them or knocks them over. Urchins may also occasionally feed on coralline algae that some aquarists may be trying to promote. If algae levels in the aquarium are low, urchins can be fed by attaching algae sheets to a piece of rock with a clip or rubber band.

Some urchins are venomous, but most species are harmless to aquarists. The most common injuries from urchins happens when the aquarists bumps against an urchin and gets poked by its spines. Spines can become broken off in the skin, especially with thinner-spined urchins, so always take care around your urchin to avoid injuring it or yourself.