Glaucus atlanticus, commonly known as the 'blue dragon' or 'sea swallow,' is a species of nudibranch. It is a pelagic creature, which means it lives in the open ocean rather than on the seabed. Glaucus atlanticus is renowned for its striking blue coloration on its dorsal side, which helps it blend in with the blue surface of the ocean when viewed from abobe. Its underside is typically silver or gray.

This nudibranch has a unique and fascinating lifestyle. It preys on other pelagic creatures, including the Blue Button Jelly and the Portuguese man o' war, a jellyfish-like organism, by feeding on their tentacles. Glaucus atlanticus is resistant to the tentacles of the Portuguese man o' war and can also absorb their nematocysts, using them for its own defense.

You should avoid touching it with bare hands due to its nematocysts, which it acquires from its prey.