Take a close look at the fish in the photo below, and the small openings above its mouth that look like sleepy eyes... now step back a bit and take another look: those “eyes” are actually olfactory glands, and its real eyes are those huge green orbs floating inside a transparent head.
Photo by National Geographic
The head of the Pacific Barreleye (species Macropinna microstoma) is basically a clear canopy filled with liquid, which allows the fish to see in extreme low-light conditions. The eyes can pivot at nearly any angle like motorized cameras, giving it an extreme advantage over its prey by picking up the faintest reflection or shadow of movement, then triangulating on its target.
Photo by National Geographic
Although it's basically a carnivorous stealth submarine, the barreleye is actually extremely fragile at levels above its natural habitat (2,000 feet or more below the surface), so not many intact specimens have been found. This footage, captured by the Monterey Bay Aquarium Research Institute, is one rare exception: