Coleman's shrimp. Pair of Coleman's shrimp (Periclimenes colemani) on the body of a venomous fire urchin (Asthenosoma varium). This shrimp is found exclusively on this sea urchin, whose poison provides them with protection from predators. The host urchin is not harmed by the shrimp, nor does it derive any benefit from carrying it. This type of relationship is called commensalism, a type of symbiosis. The female is the larger of the two. Photographed off Ambon, Indonesia.