Arthropoda: Crabs, Shrimp, and Barnacles

Without a doubt, the arthropods are the most sucessful group of animals to inhabit the earth. They have penetrated every nook of every habitat, terrestrial and aquatic, on this planet. Three quarters of all species on the planet are arthropods. How is this possible? A brilliant body plan. The arthropods have a tough exoskeleton that can thwart the digestive juices of many other creatures: it is resistant to acids, alkalais and many other solvents. Their appendages have evolved many ingenious adaptations. For instance, the anemone crab at the top of this page sweeps plankton with its "net" claw. How can you identify an arthropod underwater? All have jointed legs, and an exoskeleton which they must periodically molt.

(click on photo to enlarge)
Barnacles
	Giant Acorn barnacle (Balanus nubilus) This is one of the worlds largest barnacles, growing up to 4" high and 5" wide. It is quite common, but prefers areas with some current and a substrate to latch onto. In rocky current areas you might stumble upon large aggregations of hundreds of these arthropods.
Crabs
	Blackeyed hermit crab (Pagurus armatus)
	Dungeness crab (Cancer magister) There are more of these guys in Washington State than there are people! A common crab in mud and silt areas, you can distinguish it from the red rock and the slender cancer by the serrated top portion of the claws which are white.
	Graceful cancer crab (Cancer gracilis) Often confused with the Dungeness, but much smaller, this cancer crab has a carapace whose teeth are lined with white. It will grow to a maximum of about 4.5 inches wide.
	Graceful kelp crab (Pugettia gracilis)
	Heart crab (Phyllolthodes papillosus)
	Helmet Crab - Telmessus cheiragonus When diving over kelp, the helmet crab is often present, but well hidden. Its carapace grows to 4 inches wide, is yellowish in color, and has a hairy appearance.
	Widehand hermit crab (Elassochirus tenuimanus)
	Puget Sound King crab (Lopholithodes mandtii) This is surely the king of all Northwest crabs (hence the name). They grow to a whopping 12" across, and that is only the carapace! Look for these crabs in the higher current areas of the San Juans, and the Strait of Juan de Fuca.
	Northern Kelp crab (Pugettia producta) A common site while diving in most habitats, this crab has a olive to reddish carapace and long graceful legs. The female has much more slender claws than the male. You can distinguish it from similar looking species by its smooth carapace, which is usually not "decorated".
	Red Rock crab (Cancer productus) This is one of our most common crabs. Many mistake it for a Dungeness Crab. You can tell the difference between the two by the claws. A red rock has black tips on the end of the claws whereas the those of the Dungeness are white tipped.
Shrimp
	Spot prawn (Pandalus platyceros) This is an enormous shrimp that you will most likely see at night,or in deeper waters on sandy and silty bottoms. It is flesh colored, and has a white spot on both sides of the carapace, present on its first and fifth segments.
	Stiletto shrimp (Heptacarpus stylus)
	Coonstripe shrimp (Pandalus danae) If you see a shrimp in the Northwest, chances are you are looking at the Coonstripe. It is our most common shrimp and can be found in a wide range of habitats. Look for the irregular dark zig zag stripes on the carapace for a positive ID.