Decapods are crustaceans (joint-legged marine animals) and include the crabs and shrimp. Look closely, and you can see that they have similar jointed legs, nippers (or claws), and antennae! Crabs are protected by a thick shell (or carapace), and those strong nippers. They swim when they are young, but as adults can only walk and climb. Shrimp swim, and have more delicate exoskeletons composed of thin translucent plates.
.
Flattop porcelain crab 
Petrolisthes eriomerus
Look for: Round carapace
Reddish brown to vibrant blue
Exceptionally large, flat nippers
Very long thin antennae
Small: No more than 2 inches
Diet: Suspension feeder
(play video at right to see the porcelain crab feeding)
Abundance: Seasonal, April to June
Notes: The porcelain crab gets its name from its tendency to drop claws,
just like a fragile tea cup. The discarded limb is meant to
distract a would-be predator. The crab will soon molt and
re-grow the lost appendage.
Purple shore crab 
Hemigrapsis nudus)
Look for: Oblong purple carapace
Eyes wide apart
Nippers tucked under “chin”
Not aggressive
Small: No more than 2 inches
Diet: Grazer (algae, diatoms), scavenger
Abundance: Common
Green shore crab 
(Hemigrapsis oregonensis)
Look for: Oblong greenish yellow carapace
Eyes wide apart
Nippers tucked under “chin”
Not aggressive
Small: No more than 2 inches
Diet: Grazer (algae, diatoms), scavenger
Abundance: Common
.
Helmet crab 
(Telmessus cheiragonus)
Look for: Triangular carapace
Eyes close together in middle
Bristly exoskeleton
Yellowish green
Diet: Small invertebrates, algae
Abundance: Seasonal, April to May
Northern kelp crab 
(Pugettia producta)
Look for: smooth carapace, green above
Underside yellow and red
Long thin legs
Large: can be 6-12 inches
Diet: small invertebrates
Abundance: Common
Decorator crab 
(Oregonia gracilis)
Look for: narrow, pointy carapace
Two long rostral horns
Very thin long spidery legs
“Decorated” with sponges and algae
Small: under 2 inches
Usually seen in eelgrass
Diet: small invertebrates, algae
Abundance: Scarce
Dungeness crab 
(Cancer magister)
Look for: Fan shaped pinkish carapace
Eyes close together, short antennae
Ten “teeth”- last at widest point
Juveniles can be white, black, mottled
Aggressive, threat posture
Large: carapace can be 9 inches
Diet: clams, snails, barnacles
Abundance: Common
Graceful crab 
(Cancer gracilis)
Look for: Fan shaped pinkish carapace
Eyes close together, short antennae
Ten “teeth”- last below widest point
Juveniles can be white, red, mottled
Aggressive, threat posture
Large: carapace can be 5 inches
Diet: clams, snails, barnacles
Abundance: Common
Red rock crab 
(Cancer productus)
Look for: Fan shaped red carapace
Eyes close together, short antennae
Nine “teeth” on each side of carapace
Juveniles can be finely striped
Black-tipped claws
Aggressive, threat posture
Large: carapace can be 8 inches
Diet: clams, snails, barnacles
Abundance: Common
.
Pacific rock crab 
(Cancerantennaria)
Look for: Fan shaped pink/red carapace
Eyes close together, short antennae
Nine “teeth” on each side of carapace
Red spotting on underside
Black-tipped claws
Juveniles: dense hair on carapace
Aggressive, threat posture
Large: carapace can be 7 inches
Diet: clams, snails, barnacles
Abundance: Scarce
.
Pygmy rock crab 
(Canceroregonesis)
Look for: Oval red/brown carapace
Eyes close together, short antennae
Nine “teeth” on each side of carapace
Black-tipped claws
Very hairy legs
Aggressive, threat posture
Large: carapace under 2 inches
Diet: clams, snails, barnacles
Abundance: Scarce
Black-clawed crab 
(Lophopanopeus bellus)
Look for: Oblong reddish/brown carapace
Looks like a shore crab
Thin black claw fingers
Very aggressive
Small: up to 2 inches
Diet: clams, snails, barnacles
.
Coonstripe shrimp 
pandalus hypsinotus
Reddish to pink body with white spots near head.
Fine wavy light and dark lines on tail.
Long candy-cane striped antennae.
Delicious: one of our most popular seafoods!
Abundance: Seasonal, May to June
Friday Harbor Marine Health Observatory 