Looking for a unique invertebrate to add to your saltwater tank, consider the sea urchin.
Sea Urchins are approximately 2"-3" in diameter, with the spines extending possibly twice that distance, that can be found in a variety of saltwater habitats around the world. These creatures belong to the class Echinoidea in the phylum echinoderm which contains over 900 different species. Common colors include black and dull shades of green, olive, brown, purple, and red.
Not only are sea urchins a unique and interesting creature, but they also make great additions to marine aquariums, consuming undesirable algae and detritus within the tank. Care must be taken to prevent the Urchins from accidentally overturning rocks in the reef tank causing damage to themselves and other reef inhabitants such as live corals.