Sindromeda is one of the twenty-three worlds of the Vega star system. The native Sindromedans were muated by Psions experiments with the gas cloud that surrounds the planet. The other race that exists on the planet is the Graffalloons, who managed to stay unaffected by the genetic change.
But there is a third intelligent race on Sindromeda, one located in the south continent of the planet and who was, in times, the same that the north Sindromedans. Through 400,000 years of split evolution, the south Sindromedans diverged from their northern counterpart, and were thus unaffected by the violence awakening gas.