Meet Glaucus Atlanticus, also known as the Sea Swallow and the Blue Sea Slug. Pretty, isn’t it? You can find it pretty much everywhere in the warm areas of sea. It floats upside down on the surface tension of the water. Like a lot of slugs the Glaucus Atlanticus is a hermaphrodite and when it mates both partners produce eggs.
But Glaucus Atlanticus is another gorgeous example of how beauty can be deceiving; it is a ruthless predator. It routinely eats poisonous Man o’ Wars that are at least three times its size. It’s immune to the poison and indeed eats the nematocysts that produce the poison, apparently choosing the most poisonous ones to boost its own poison production. And when no other prey is available, Glaucus Atlanticus is known to become a cannibal. The feather-like appendages act as its poison storage and since it stores the poison it packs a bigger punch than the Man o’ War so if you see one it’s probably a good idea not to touch it.