The crown of thorns starfish (Acanthaster planci) is a large, multiple-armed starfish that preys almost exclusively on hard, or stony, coral polyps. It gets its name from the venomous thorn-like spines that cover its upper surface. It can be found all throughout the Indian and Pacific Oceans but is most common around Australia. It can reach a maximum size of up to 14 inches (36 centimeters) and can have up to 21 arms. The crown of thorns has a ravenous appetite for coral and armies of these starfish have been known to decimate coral reefs around Australia.