Not only do these blue sea slugs look fierce, but they actually are. These striking creatures feed on dangerously venomous prey, the most notorious example of which is the Portuguese man-of-war—an invertebrate whose stinging tentacles are excruciatingly painful for humans. 

How do they resist the man-of-war's torturous sting? They transport the toxin to specialized sacs at the tip of their finger-like appendages and store the venom for their own use.

The blue sea slugs (Glaucus atlanticus) were first discovered by Captain Cook on his second voyage to the Pacific. The top of the animal's body is blue to protect itself from predators such as birds, while its belly is silver to camouflage it from hungry fish below. 

The species float by swallowing air and storing it in their stomach, the location of which makes the species drift upside down. Check out a video of the marvelous creature below: