"Coral crab" is a general, unscientific term referring to those crabs which depend on a coral for shelter and livelihood, including either soft or hard corals. This particular crab is small-- under an inch across. It takes shelter between the finger-like branches of a hard coral formation, such as those found in the shallow portions of a healthy reef. Typically, small crabs such as these retreat to the deeper, harder to reach recesses of a coral when approached. This makes them difficult to photograph, but I happened to catch this one in the open and was able to get a good shot.
Sometimes crabs will have one claw that is much larger than the other; the heavy claw is used for crushing and the smaller claw is for cutting. This one is holding its smaller right cheliped close to its body.
Identification: Trapezia rufopunctata *
*[special thanks to J. Poupin and Dr. Peter Castro for assistance with photo identification]