My porcelain crab came out today in a spot where I could easily take a picture. He is a nice looking blue and red crab with large claws. Despite the claws, he is a docile crab that feeds by waving extended combs (setae) in the current to catch plankton and other small bits of food. Here is a close-up of his combs:
"The porcelain crab's common name is derived from its propensity to drop claws like a fragile tea cup breaking. When attacked, the would-be predator is usually left with nothing more than a few amputated (and still-twitching) limbs. In a few days the porcelain crab will undergo an 'emergency molt' of its exoskeleton and begin regenerating its lost appendages.
The porcelain crab shown here, Petrolisthes galathinus, is a common resident of Floridian and Caribbean reefs, living under rubble and coral heads. Turning over loose rocks will often yield a fleeting glimpse of scurrying, purple legs. They can move incredibly fast and generally remain cryptic to the passing scuba diver. While many crab species are territorial and agressive towards members of their own species, these porcelain crabs can be colonial with several dozen porcelain crabs living together under the same rock.
Despite the similar appearances, porcelain crabs are not 'true' crabs; they are in fact more closely related to the squat lobster clan (Galatheidae) than the archetypal brachyuran crabs we are all familiar with. Porcelain crabs' flattened bodies are adapted to their life under rocks and in crevices. One of the defining features of porcelain crabs are the comb-like appendages called 'setae' that sweep the water currents in order to collect edible particles that happen to float by. Another pair of specialized appendages scrape the the setae and bring the collected food to their mouthparts. This feeding strategy, with its alternating rhythm, appears robotic in its efficiency." (excerpt from http://coralmorphologic.com