A nicely patterned Foliate Kelp Crab (Mimulus foliatus) photographed at Pinnacle Gulch. This was a small individual, the carapace was only ~2 cm (3/4 inch) across.
Note the flared leaf-like points on both sides of the carapace and the red-and-white striped hind legs.
And if you look closely you should be able to see that this crab has decorated its rostrum — the portion of the carapace that extends forward in front of the eyes, which are light pink in this crab. It has stuck small bits of seaweed (and other material that I can't identify) to tiny hooks to camouflage itself against visual predators such as fish and octopus.
I first wrote about Foliate Kelp Crabs on 14 May 2012 (during a trip to Oregon), so if you'd like to learn more about them, you can read that post here.