Introductionflatfish, common name for any member of the unique and widespread order Pleuronectiformes containing over 500 species (including the flounder, halibut, plaice, sole, and turbot), 130 of which are American. Flatfishes are common in both the Atlantic and Pacific; many are important food and game fishes. All flatfishes have an unusual flattened body form well suited to life on the bottom. The development of the young flatfish recapitulates to some degree the probable evolutionary process. The newly hatched transparent larvae are bilaterally symmetrical, but soon the characteristic compression of the body develops and one eye "migrates" to the other side of the head—either the left or the right, depending on the species. Changes occur also in the skeletal and digestive systems; adults have only one dorsal and one anal fin, both without spines. The underside of the flatfish is pale and the top is colored to match the environment; some species, especially the flounders, are able to change their pigmentation. Flatfishes are divided into two groups: the soles, families Soleidae, Cynoglossidae, and Achiridae; and the flounders (including the halibuts and others), families Bothidae and Pleuronectidae.
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