Saturnyne was the home of the Saturnynians. It had a large body of water, judging by the amphibious nature of its dominant species. The planet had considerable technology and knew, including weather control, perception filters. They also knew about Gallifrey and the events of the Last Great Time War.
At some point in the planet's history, it fell to a mysterious crack in space and time that consumed its skies. The planet was lost to what a member of its species, Rosanna Calvierri, referred to as "silence". A large number of its species escaped the planet through the crack to 16th century Venice. They planned to turn the city into the new Saturnyne. (TV: The Vampires of Venice)