Glaucus atlanticus (blue sea slug)

These little guys are pretty awesome. They live in temperate and tropical waters, staying afloat by swallowing air and keeping it in their stomachs. They eat the venomous Portuguese Man o’ War jellyfish and keep its stings for their own defence. And they look like cycloptic alien dragons. What’s not to love?

(Photos and info from Wikipedia, the Natural History Museum and Animals Talking in All Caps.)

Edited to add: Here’s what they look like on the inside!