A crayfish twice as big as any that has ever been seen crawled out from under a rock in the deepest part of a Tennessee creek. "This isn't a crayfish that someone would have picked up and just said, 'Oh, it's another crayfish,'" said one aquatic biologist. The new crayfish is about five inches long and has long, bristle-covered antennae. Its tail features a splashy spread of aquamarine highlights. There are over 600 species of crayfish in North America, but this one shocked scientists and reminded researchers that undiscovered species can live on even in populated, well-explored areas.