The black rock urchin, Arbacia sp, is a rather uncommon urchin for the Atlantic side of the Keys, but it seems to be having an unusually good year there. I haven’t been able to find an accurate description and picture of his urchin, and when I have found a picture, the scientific name is wrong, so I don’t have the exact species name of it. This is a great algae eating urchin that is very attractive and showy in an aquarium. It very rarely hides, but instead spends its days crawling all over the rocks and walls of the tank looking for algae. They will get as big as 4 inches in diameter, but we sell just the small ones that are about 1 inch in diameter. It’s a deep purply black color with long sharp spines, similar to Diadema antillarum but not quite as long and a little stronger.