a subspecies of humans who lived in giant cities built in caverns under the sea, believed to be the descendants of the ancient civilizations of atlantis, lemuria, and mu with traces of their greco-roman-like culture on easter island. they are also on friendly terms with the aliens of m space hunter nebula. the seatopians revere megalon as their god, awakening him to attack the surface after their capital city was devastated as the result of a nuclear test carried out near the aleutian islands and destroyed monster island. the seatopians send an invasion squad to acquire the robot jet jaguar to function as megalon's guide before the robot's creators wrestle back control before jet jaguar becomes self-aware enough to act on his own to help godzilla drive off megalon and gigan. the seatopians seal their entry points with the humans deciding not to retaliate against them.