Fish
. Fish, diverse group of animals that live and breathe in water. All fishes are vertebrates (animals with backbones) with gills for breathing. Most fish have fins for swimming, scales for protection, and a streamlined body for moving easily through the water. Fishes may be divided into two distinct groups, jawless fish and jawed fish. The jawless fish are represented by two families of distantly related eel-like fish, the hagfish and the lampreys . Both fishes have tongues equipped with numerous small teeth and lack paired fins and a bony skeleton. Although these two families include only a handful of living species, the fossil record shows they were once a highly diverse group that also included fish whose head and trunk were covered with a hard bony shell. Hagfish are the vultures of the abyss, feeding on carcasses of dead fish and other animals. Lampreys, in contrast, feed on live fish by attaching their sucking disk to their host and rasping away tissue with their toothed tongue.