You Can Literally See What’s Going Through This Fish’s Head
Meet Macropinna microstoma, a small fish who appears to be totally normal — until you get to the see-through head.
See those little things at the end of his face that look like cute, sleepy eyes? Those are his nostrils, or at least organs that help him smell. His real eyes are the brownish tubes inside his head, ending in those bright green half spheres.
M. microstoma is a species of barreleye — a type of fish named for their tubular, barrel-shaped eyes. The species developed their transparent heads and tissue to help them navigate the murky depths of their ocean home, more than 2,000 feet below the surface.
According to MBARI, the roughly 6-inch fish spends most of the day hanging motionless in the water — thanks to his large, flat fins — with his eyes pointed upwards to sense the silhouettes of possible prey. When the fish sees something edible, he switches his body into a vertical position to nab it, swiveling his tubular eyes forward so he doesn't lose sight of his meal — which is where the clear head comes in handy.
Scientists at MBARI have also speculated that the green lenses on his eyes help block sunlight, allowing him to focus on the bioluminescence of potential prey.
Of course, that still doesn't explain why his eyes are actually inside his head. But since M. microstoma shares his home with siphonophores — jellyfish-like animal colonies that sometimes look like long, translucent tubes covered in stinging tentacles — scientists think that the protective head may allow the barreleyes to pick off food from the siphonophores' tentacles without their eyes getting stung.