Illinois Natural History Survey - University of Illinois




Carolyn Nixon


Many species of crustaceans live in Illinois, most of them in or near the water. See if you can match the

drawings on the left with the names and descriptions of the groups of common crustaceans that can be

found in Illinois. Write the letter of each animal in the blank on the left of its matching description below.



Cshrimp.png FairyShrimp.pngD


pillbug.pngE ostracod.pngF



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1. Fairy shrimp (anostracans) appear to swim upside-down, with their many swimming legs reaching upward from the body. They only appear after spring rains and must complete their life cycle before the pools dry up. The eggs withstand drying and freezing to hatch when the area floods again, sometimes years later.

2. Crayfish (decapods) have 10 pairs of legs. The first pair has large, pincherlike claws or chelae. They resemble lobsters.


3. Freshwater shrimp (decapods) have 10 pairs of legs like their crayfish cousins, but the pincherlike claws are much smaller. They are slightly flattened laterally (from side-to-side).


4. Water fleas (cladocerans, such as Daphnia) are round, tiny crustaceans that swim with their long antennae. They give birth to live young, which can be seen inside the transparent shell of the mother.


5. Water fleas (copepods, such as Cyclops) are tiny crustaceans that are difficult to see without a microscope, and are considered plankton. They have large heads that taper to an elongate body. There is often a single eye on the head.


6. Seed shrimp (ostracods) are tiny crustaceans that have their entire body enclosed within a clamlike shell. The shell has two halves that are hinged along the back. They often crawl along sediment or vegetation in water. They sometimes swim in the water column by beating their antennae.


7. Pill bugs and sowbugs (isopods) are either aquatic or terrestrial. The terrestrial species are usually found in moist areas, such as under logs and leaf litter. The pill bugs can roll into a ball when disturbed.


8. Scuds or side swimmers (amphipods) are small, shrimplike crustaceans that burrow in loose sediment and plant debris in still water. They are very flat from side to side and scuttle along through the sediment on their sides.

ANSWERS—From next page

1-D, 2-H, 3-C, 4-A, 5-B, 6-F, 7-E, 8-G


Drawing credits: Drawing credits: A, B, F, G, H

by Carie Nixon; C from The

Crayfishes and Shrimp

(Decapoda) of Illinois; and D,

E from Dover Clip-Art

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