Crayfish are crustaceans that are also known as crawdads, crawfish, and freshwater lobsters. they are closely related to lobsters, crabs, and shrimp. There are about 150 crayfish species in North America, and over 540 species worldwide.
The body of a decapod crustacean, such as a crab, lobster, or prawn (shrimp), is made up of twenty body segments. They are grouped into two main body parts, the cephalothorax and the abdomen. Each segment may have one pair of appendages. In some groups these may be reduced or missing. On average, crayfish grow to 17.5 centimetres (6.9 in) in length, but some grow larger. Walking legs have a small claw at the end.
Crayfish live in streams, rivers, swamps, ponds, and other freshwater habitats. Most crayfish are strictly aquatic but some live in semi-aquatic environments. The semi-aquatic crayfish burrow into the soil to get to water (so that they can breathe). Some can also be put in private aquarium to be used as pets
Crayfish are omnivores; they eat plants, animals, and decaying organisms. They are nocturnal (most active at night) and eat fish, shrimp, water plants, worms, insects, snails, and plankton. Larval crayfish are very tiny; they eat plankton.
- Thomas Henry Huxley (1880). The Crayfish: an introduction to the study of zoology. New York: D. Appleton & Co.