Though no formal name has ever been attributed to them, these were a race of highly evolved, sentient jellyfish. They despised the notion that the seas were dominated by the humanoid Atlanteans, and embarked upon an ambitious plan to insure racial purity in their territories. They bided their time until Atlantis was at its most vulnerable, when its capital city Poseidonis was under the command of an inept leader named Pletus. The Jellyfish commandeered ships and transport craft and began their invasion. They always concealed themselves within metal shells, so that nobody ever knew what the invaders actually looked like.