The Pacific barrel-eye fish has a see-through head

Their barrel shaped binocular-like eyes have adapted to serve them well in the deep ocean. Not only can their eyes can detect silhouettes from crustaceans above, they can also differentiate between ambient light and bioluminescent light emitted from other such ocean dwellers. Scientists used to believe that the fish’s eyes were stationary; however, now scientists assert they they can direct their eyes forward too. This fish was initially discovered in 1939, and at the time nothing much was known about them.

 
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