Discover writes about evolution in action.

Sometimes a species is so complex, so marvelous, or simply so weird that it’s hard to imagine how it could have possibly evolved by natural selection. Among the weirdest is the flounder.

Not many animals would be at home in a world made by Picasso, but the flounder would fit right in. It belongs to a group of fish called flatfish, or pleuronectiforms, that all spend their adult lives hugging the sea floor, where they ambush smaller fish. Flatfish are teleosts, a huge group of fish species that include more conventional creatures like trout and goldfish. While they have a lot of teleost anatomy, flatfishes also have some bizarre adaptations for their life at ninety degrees. All vertebrates, ourselves included, use hair cells in the inner ear to keep ourselves balanced. In most flatfish species, the hairs have rotated so that swimming sideways feels normal to them. Many flatfish can camouflage the upward-facing side of their body. The underside is pale, and in many species the fin is tiny.

And then, of course, there are the eyes.

Read on.