Black Longspine Urchin – Diadema setosum

The Black Longspine Urchin (Diadema setosum) is popular and has a very well-known appearance. It has long, thin black spines that extend from its body, and five rows of electric blue spots in asymmetrical design on the body. The anus of the urchin looks like an eye on the top of the body, with a bright orange ring in the center. While the body itself is usually only about 2 to 3 inches in diameter, the spines can make this urchin up to 12 inches across.

The spines on this urchin can break off easily and become embedded in the skin of a tankmate (or an aquarist) that bumps against them. Take care when maintaining the aquarium to avoid bumping against this urchin or its spines and do not place it in a small aquarium where it may come into contact with crowded tankmates. These urchins are mildly venomous. The venom is very mild but wounds from this urchin can still be painful as the spines themselves are needle-like and covered in bacteria so wounds can easily become infected quickly.

These urchins are grazers that will roam about the tank searching for food and algae on the substrate and rockwork. They will not actively eat corals, but some delicate corals may be damaged if the urchin crawls on top of them or knocks them over with its long spines. Urchins have also been known to eat coralline algae desirable to some aquarists.