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The crayfish and the fairy shrimp, The copepod, the water flea, The sow bug, and the little scud Wear shining armor constantly. A student noticed this, and so Named them crustaceans, long ago.
CRAYFISH, fairy shrimp, insects, spiders, and mites belong to a large group of animals known as arthropods. You know from your study of the crayfish that the suffixes ped and pod mean feet. Arthro is taken from a Greek word meaning joint. Therefore, the arthropods are the "joint-footed ones."
The joint-footed animals are divided into a number of different classes. Crustaceans make up one class, insects another, and so
on. The crustaceans are the arthropods with a crust-like covering, or shell, or the "crust-covered, joint-footed ones."
Crayfish and fairy shrimp are crustaceans. Scientists call crayfish decapods. If you know what the prefix deca means, you can see where the name originated. A crayfish is, literally, a "joint-footed, crust-covered, ten-footed one"!
When you are searching for fairy shrimp, you may find other small crustaceans, such as amphipods, isopods, and copepods.
AMPHIPODS
Amphipods are commonly called scuds, perhaps because they move swiftly along like a small vessel driven before a gale. They can also jump, and for this reason are sometimes confused with minute crustaceans called water fleas. Scuds are commonly from one-eighth inch to one-half inch in length, and are often pale green in color. They can readily be distinguished from the crayfish and fairy shrimp by their flat, flea-
like appearance. They will stay alive a long time in an aquarium, where some species can be observed eating decayed plant and animal matter. The amphipod in the photograph was one of several brought up in a dip-net, clinging to a dead fairy shrimp.
WATER FLEAS
The water fleas most commonly seen are tiny, flat-looking crustaceans, about as large as the head of an ordinary pin. They appear to be circular or oblong animals, but a microscope or a good hand lens will reveal a variety of shapes. They feed on microscopic forms near the water's surface. Their bivalve shells are transparent, and the heart, the alimentary canal, and eggs, when eggs are present, can be plainly seen. This fact will usually distinguish the water flea from the Ostracod, another minute crustacean whose bivalve shell is not transparent, and who, as he swims through the water, looks like an animated seed.
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