Paralichthyidae, Bothidae, Achiridae, and Cynoglossidae - flatfishes
Flatfishes are bottom-feeding "flat" (laterally compressed) fishes that swim on their sides and often bury themselves under the bottom sediment when at rest. Initially, a flatfish egg develops into the typical fish-like shape, and the eyes are on both sides of their head. At less than one inch, one eye migrates to the other side (either left or right), and the mouth and internal organs rearrange to form the typical flatfish body shape. The side of the fishes that hugs the bottom is referred to as the "blind" side. It is usually whitish, but can exhibit a variety of colors and patterns. On the "ocular" side, flatfishes have the ability to change their body coloration and patterns to match their surrounding backgrounds, thus camouflaging themselves from predators and prey.
There are four families of flatfishes in the Gulf of Mexico. Paralichthyidae, Bothidae and Cynoglossidae have eyes on the left side of their bodies. Family Paralichthyidae are called sand flounders. They are football shaped (wider in the middle) generally with distinct snouts. Bothidae, the lefteye flounders, are most like the sand flounders but can be distinguished by their long pelvic fin bases (one or both fins) and the asymmetry of the pelvic fins, among other things. Tonguefishes, in the family Cynoglossidae, are oblong-shaped, blunt at the snout with a pointed tail at the other end. Soles, belonging to the family Achiridae, are right-eyed. Their bodies are round with no distinct snouts. Both soles and tonguefishes have gill plates that are covered with skin and scales. Another family of flatfishes, Poecilopsettidae (specifically the deepwater dab, Poecilopsetta beanii) may occur in the Gulf but only from very deep waters. Flatfishes can be further distinguished by the shape of their lateral line, the size of their mouths, and pigment patterns on their bodies.