Honestly, you'll have to post a better picture than what you've posted already, before anyone can even attempt to help you. I can't even be sure where the crab is, let alone trying to ID it.
(Reminds me of a contest the Vancouver Sun ran in the '70s called "Where's The Puck". A picture of game action of the Canucks would be run, with the puck removed. The object was to guess where the puck was).
Cheers,