|This crab is commonly found in
shallow water near or above the surface, hiding among
narrow rock crevices. Flat rock crabs are extremely
quick, moving so fast with their sideways motion they are
often difficult to identify. Their speed and elusiveness
make them unlikely photo subjects.
This particular specimen seems to be short a few limbs (nobody is that quick with a shutter).
Identification: Percnon planissimum