Any fish species in the order Pleuronectiformes, which includes flounders, flukes, dabs, halibuts, plaice, soles, and turbots. All flatfishes have an unusualy compressed body form adapted to life on the bottom. As the bilaterally symmetrical immature forms develop, one eye migrates to either the left or right side, depending upon the species. The body compresses laterally with changes in the skeletal and internal organ systems, and the animal rests on either its left or right side. The side on the bottom is pale, while the other side is strongly pigmented. Some species are able to change their pigmentation to match the appearance of the bottom.