Untitled Sea Devil film (unproduced home video)
From Tardis Wiki, the free Doctor Who reference
Around the time he had the idea to create Return of the Sontarans, Kevin Davies also had plans to create a Sea Devil film. The film was to feature a brand new type of Silurian — a River Devil, which was going to be like a Sea Devil, only more enhanced with more prosthetics on the face and when it opened its gills. (REF: Downtime – The Lost Years of Doctor Who)