Characteristics thumb|left|Flatfish are asymmetric, with both eyes lying on the same side of the head thumb|left|European flounder, like other flatfish, experience an eye migration during their lifetime. The most obvious characteristic of the flatfish is its asymmetry, with both eyes lying on the same side of the head in the adult fish. In some families, the eyes are usually on the right side of the body (dextral or right-eyed flatfish), and in others, they are usually on the left (sinistral or left-eyed flatfish). The primitive spiny turbots include equal numbers of right- and left-sided individuals, and are generally less asymmetrical than the other families. Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the seabed (benthos), and the extension of the dorsal fin onto the head. thumb|Polynemus, a threadfin, belongs to the same group as flatfish, but looks completely different The most basal members of the group, the threadfins, do not closely resemble the flatfishes.
Characteristics thumb|left|Flatfish are asymmetric, with both eyes lying on the same side of the head thumb|left|European flounder, like other flatfish, experience an eye migration during their lifetime. The most obvious characteristic of the flatfish is its asymmetry, with both eyes lying on the same side of the head in the ad,ult fish. In some families, the eyes are usually on the right side of the body (dextral or right-eyed flatfish), and in others, they are usually on the left (sinistral or left-eyed flatfish). The primitive spiny turbots include equal numbers of right- and left-sided individuals, and are generally less asymmetrical than the other families. Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the seabed (benthos), and the extension of the dorsal fin onto the head. thumb|Polynemus, a threadfin, belongs to the same group as flatfish, but looks completely different The most basal members of the group, the threadfins, do not closely resemble the flatfishes.