The Marvostians are an original species. In my Sargon and Beyond campaign, they are also members of the Wairara League, and their planet is in the Cordon Nebulae alongside the Wairara colonies. They are a two-headed species, who always remain in their sealed environmental suits when off-world. They are always prepared with redundancies, enjoy singing, and often talk with both heads at once.
You may place them anywhere in your campaign.