Crustacea

THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

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

fdsf

Identify taxa Jointed legs

Crustacea


	Subphylum Crustacea (crustaceans) Class/Order Key \| Class/Order List
	Crustacea are probably one of the most recognizable groups of macroinvertebrates. The crayfish in particular are large, active, and often brightly colored, making them easy to see for anyone peering into the waters along the edge of a stream or lake. In wetland samples in the Northwest, Crustacea likely to be found include seed shrimp, water fleas, sowbugs, copepods, scuds, and maybe even crayfish or fairy shrimp. The greatest diversity of crustaceans is in marine and estuarine environments, but a few live on land (pill bugs or roly polies) and many live in freshwater or wet terrestrial habitats (crayfish, sowbugs, scuds, freshwater shrimp, tadpole shrimp, and others). Some take advantage of extremely temporary water sources; fairy shrimp are well known for developing rapidly in vernal desert pools after a rain, then laying eggs that are dormant until the next rain pools enough for them to complete their short life cycle. Species like the fairy shrimp can be very sensitive to habitat modifications, but many other types of Crustacea are quite tolerant. Scuds and sowbugs are often found in urban waterbodies where most other macroinvertebrates have vanished. Crayfish can also deal with substantial changes in their surroundings. Unfortunately, this high level of tolerance to habitat changes allows some crustaceans to be easily transported and invade new habitats. Crayfish have been introduced to the Pacific Northwest from the Midwest, Southeast, and around the world. Smaller introduced crustaceans like copepods regularly become part of our aquatic communities through ship ballast, boat motors, and other means. The Chinese mitten crab has been introduced via the aquarium trade. Unfortunately, these introductions have caused substantial harm to native crustaceans and other aquatic and terrestrial animals. Read more about the introduced crustacea in the west.

Class/Order Key

	Amphipoda (scuds) medium sized; body flattened from side to side; legs extend out to one side when viewed from above; legs are not enclosed in an expanded carapace.

	Branchiopoda (fairy and clam shrimp, water fleas) wide variety of physical characteristics and behaviors; most live in fresh or brackish water, and many inhabit temporary vernal pools.

	Copepoda (copepods) Tiny crustaceans; benthic forms generally slender with short antennae; pelagic forms are teardrop-shaped with long antennae; may have a single reddish eyespot in the front of the head.

	Decapoda (crayfish, crabs, shrimp, prawns) Can be quite large with well-developed, muscular flipper-like tail; long pointed rostrum extends from front of head; large eyes on moveable stalks.

	Isopoda (sowbugs) medium sized; body flattened from top to bottom; legs either hidden underneath or sticking out to both sides when viewed from above; may roll partially into a ball when disturbed.

	Ostracoda (seed shrimp) small, clam-like crustaceans that look like grayish-white seeds or jelly beans; may be a single dark eye and a few legs visible through the bivalved shell.

	Crustacea uncommon in wetlands Cumacea (cumaceans): marine; near mouths of coastal streams Mysidacea (opossum shrimps); downstream of still waters; coastal streams

Class/Order List:
Amphipoda (scuds)
Branchiopoda (fairy shrimp and relatives)
Copepoda (copepods)
Decapoda (crayfish)
Isopoda (sowbugs)
Ostracoda (seed shrimp)
Cumacea (cumaceans) - marine; near mouths of coastal streams
Mysidacea (opossum shrimps) - downstream of still waters; coastal streams

Resources

fdsf