Sea-Tron is an unreleased theme that, had it been released, would have been a subtheme of Space. The theme would have been set on an alien planet, with underwater astronauts. Many new monorail parts and colours were made for this theme, but when Futuron's monorail failed to make money, development of Sea-Tron stopped. There were also aliens designed for the theme, but the LEGO company stated that it was not yet time to have aliens.
- Sea-Tron Alien
- Sea-Tron Astronaut