On the surface of warm oceans drifts a creature barely three centimeters long that seems straight out of a mythological tale: the blue sea dragon (Glaucus atlanticus). Despite its small size and fragile appearance, this gastropod mollusk is one of the boldest predators in the plankton, capable of routinely feeding on prey that is deadly to most marine animals, including the feared Portuguese man o' war (Physalia physalis).
To support itself on the surface film of the water, the blue sea dragon swallows an air bubble that it stores in its stomach. This causes it to float in a permanent inverted position: its electric blue belly points toward the sky to blend in with the sea from birds, while its silvery back faces the depths to camouflage itself from fish. However, its true biological feat is the phenomenon known as kleptocnidy.
When devouring the tentacles of the Portuguese man o' war, the blue dragon is not only immune to the toxins, but its digestive system sorts and selects the most potent stinging cells (the nematocysts). Instead of digesting them, it transports them intact through digestive diverticula to the tips of its feathery appendages, called cerata. There they are stored in specialized sacs known as cnidosacs.
The result is astonishing: by concentrating the stolen weaponry from multiple prey, the blue dragon delivers a sting significantly more painful and lethal than that of the organism from which it obtained the toxins, turning someone else's defense into its most lethal shield.
Source: National Geographic / Marine Biology Association (MBA)
