A small specimen of Hyas araneus, apparently known as "Great Spider Crab", though around my parts more commonly known as Masking crab, due to it's habit of dressing up in colourful algae to perfect it's camouflage, as seen here, with a very stylish hairdo in red algae.

Edit: A quick reupload, mistakenly took the big-ass picture that might be a bit unwieldy :P