THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Decapoda
(crayfish, crabs and freshwater shrimp)
Key to Genera/Species | List of Genera/Species

As with most Crustacea, the greatest diversity of decapods is in the ocean. They are also abundant in freshwater habitats. Decapods do occur in the wetlands of the Pacific Northwest, although there is little information available about their specific distribution.

Some of the most recognizable of the Decapoda (crabs, prawns, lobsters) find their way to our dinner plates. Dining on decapods, whether farmed or wild caught, has had and continues to have severely negative repercussions for marine ecosystems. Crayfish tails are quite a treat and a staple for many Southern dishes. However, they have been widely introduced for use as food and tend to dramatically alter native communities where they become established.

All Decapods have10 well developed legs, with claws on at least two legs.Crabs and crayfish are flattened top to bottom, and usually have large front claws.

Freshwater shrimp in the introduced family Palaemonidae have been collected in Pacific Northwest wetlands. Freshwater shrimp don't have large front claws, and tend to be flattened from side to side with very long antennae and a well developed tail.

Crayfish may be found in Pacific Northwest wetlands. They have a well developed tail while crabs do not. Crayfish are very conspicuous, but differentiating species can be very difficult. In the Pacific Northwest. we have only one native genus - Pacifasticus- that has only a few species. However, two other genera (Orconectes and Procambarus) have been introduced - and occur in wetlands.

There is a great website that shows the occurrence of crayfish species by state (outside link).

Pacifastacus spp.
(signal crayfish)
tail is long and well-developed; body flattened top to bottom; have well-developed front claws (unless broken off); the bottom segments of the legs have no hook-like lobes sticking out to one side; never have a doughnut-like sclerite between the bases of the 4th and 5th pairs of legs

Orconectes spp.
tail and claws are well-developed; body flattened top to bottom; the species in the Rogue basin has dark and light markings and distinctive black and orange tipped claws

Eriocheir sinensis
(Chinese mitten crab) This is a highly Invasive species not yet present in the Pacific Northwest. If you think you have found one please contact your state's Department of Fish and Wildlife. Tail is small, tucked under the body, and not highly noticeable; have two large claws in front, each with a very dense patch of hairs on top.

For more information and images of the Chinese mitten crab
(outside site)

Genera/species list:
native Pacific Northwest crayfish
Pacifastacus leniusculus - native to Colombia River Basin, introduced into CA, NV, UT
Pacifastacus fortis - federally endangered (outside link); Shasta County of northern CA
Pacifastacus gambelii - CA & OR
Pacifastacus klamathensis - CA & OR
Pacifastacus connectens - OR & ID; vulnerable to extinction
Pacifastacus nigriscens - San Francisco Bay area, probably extinct

known introduced crayfish species in the Pacific Northwest
Orconectes virilis - (virile crayfish - outside link) nonnative invasive , Southwest and CA
Orconectes immunis - (calico crayfish - outside link) nonnative invasive, western MT
Orconectes neglectus - (ringed crayfish - outside link) nonnative invasive, southwest OR
Procambarus clarkii - (red swamp crayfish - outside link) nonnative invasive, widespread
Procambarus acutus - (white river crayfish - outside link) nonnative invasive, CA

other native Northwest decapods
Syncaris pacifica - (CA freshwater shrimp) endangered species in the San Francisco Bay
Syncaris pasadenae - (Pasadena freshwater shrimp) southern CA, possibly extinct

other introduced decapods in the Northwest and neighboring states
Eriocheir sinensis - (Chinese mitten crab) invasive China native, CA
Geothelphusa dehaani - (stream crab) invasive Asian native, NV and spreading
Exopalaemon carinicauda - (ridgetail prawn) nonnative invasive, CA
Exopalaemon modestus - (Siberian prawn) nonnative invasive, OR and CA
Macrobrachium sp. - (freshwater prawn) nonnative invasive, introduced to northwest MT
Palaemon macrodactylus - (oriental shrimp) nonnative invasive, CA and OR
Palaemonetes kakiadensis - (Mississippi grass shrimp) introduced in southern CA? from central US
Palaemonetes paludosa - (grass shrimp) introduced in southern CA, UT and NV; from eastern US