I have just come across the world’s coolest flatfish picture, and I just thought I would share. Apparently seven of the world’s 550 species of flounder are actually polymorphic for which side of the juvenile becomes the new “top” side in the adult flatfish. Apparently either eye can pop out and rotate to the new top. This says some rather interesting things about the developmental processes involved.
See also this random talk.origins discussion, on “Why did the flatfish’s eye move from one side to the other?,” and this funny reply, and this other random talk.origins post.