Japetella Octopus
The Japetella heathi octopus is a special kind of marine life. It is a bioluminescent species, and it looks practically invisible whenever it is underwater. Whenever it senses an enemy attack, the octopus makes itself completely transparent by changing its color to red.
This helps the octopus hide its silhouette from being spotted on the bottom of the ocean floor. They also have evolved to the point that their eyes and guts are reflective, which further cuts down on the chances of being seen.