Flounder
Let's face it, the Flounder should have been called Flathead, after all it has a flatter head than a Flathead.
But no. On second thought, Flounders don't really have a flat head at all - they actually have a thin head. Yes they lie on their side and both their eyes have moved to be on the top side. To be honest it's a bit weird. It's no wonder they flounder a bit when they swim.