National Geo: Transparent Amazonian Fish
It’s speculated that the combination of its nearly invisible nature and nocturnal ways may be the reason why Cyanogaster noctivaga wasn’t discovered until recently. The fish is also tiny, measuring an estimated maximum of 0.7 inches (17 mm) long and makes its home in the notoriously murky Rio Negro, which may have contributed to its elusiveness.
Being that hard to see confers obvious survival benefits as a form of camouflage, so it’s not surprising that when it comes to transparency it *ahem* clearly isn’t alone.
(photo: Natural History Museum)