Wanderlust World Wanderlust World Glaucus atlanticus, the "blue dragon" or "blue sea slug," is a marine gastropod mollusk—a nudibranch. It is unequivocally an invertebrate (no backbone).
It floats upside down on ocean currents, preying on venomous siphonophores (like the Portuguese man o' war) and storing their stinging cells for its own defense. Found in temperate and tropical waters worldwide.