Flatfish

Flatfish are a group of ray-finned fish belonging to the suborder Pleuronectoidei and historically the order Pleuronectiformes (though this is now disputed). Their collective common name is due to their habit of lying on one side of their laterally-compressed body (flattened side-to-side) upon the seafloor; in this position, both eyes lie on the side of the head facing upwards, while the other side of the head and body (the "blind side") lies on the substrate. This loss of symmetry, a unique adaptation in vertebrates, stems from one eye "migrating" towards the other during the juvenile's metamorphosis; due to variation, some species tend to face their left side upward, some their right side, and others face either side upward. Pleuronectidae lie on their left side, with eyes on the right. Paralichthyidae lie on their right side, with eyes on the left. The "primitive" genus Psettodes may develop into "right-facing" or "left-facing" individuals.

They are one of the most speciose groups of demersal fish. Their cryptic coloration and habits, a form of camouflage, conceals them from potential predators.