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What does reversal mean in flatfish coloration and eye position?

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Body plan and sexual dimorphism in the common sole (Solea solea) and dusky flounder (Syacium papillosum). — pleuronectiform Body plan and sexual dimorphism in the common sole (*Solea solea*) and dusky flounder (*Syacium papillosum*).

In flatfish, reversal refers to a condition where the eyes and pigmentation appear on the side of the body that is normally unpigmented (the blind side).1

Typically, adult flatfishes are asymmetrical, possessing a colored ocular side and a white, unpigmented blind side, with both eyes located on the ocular side. While this orientation is standard for a given species, reversal occurs when these features are mirrored, placing the eyes and coloration on the opposite side. This phenomenon is observed with varying frequency across different species, being relatively common in some and quite rare in others.12