I thought for a moment. OK, you call them crabs and I'll call them crayfish. But they're crabs. I smiled and let it go, remembering that the language of common names is a confusing one. New Zealanders and Australians, after all, call lobsters crayfish.
Most decapods are marine, but some shrimp, a few crabs and all crayfish live in fresh water.
Crayfish are the most successful of the freshwater decapods, evolving into more than 500 species in the world's streams, lakes and ponds. Some live under stones or debris, but others build burrows which they use for retreats and for overwintering. Most crayfish are less than 4 inches long, but one type in Australia reaches the size of lobsters. This may be why folks there use the two names differently than North Americans. Like crabs, crayfish eat most anything they can find, scavenging on dead organic matter and catching small fish and invertebrates.