The person who took this picture was unsure of what kind of crustacean it was, whether it was even a crab or lobster. I am fairly sure it is some sort of ghost shrimp or mud shrimp (Thalassinidea), although it is an unusual looking one. It seems to have a much heavier, thicker exoskeleton than I’ve seen in other thalassinideans I’m familiar with. But the tail and claws are very reminiscent of burrowing beasties.
Photo by Mountain/\Ash on Flickr; used under a Creative Commons license.