From the comments:
Random question: do you know about any other films where the entire female cast appear naked like in Sirens?
By film, I mean regular movies with regular actresses (like Tara or Portia), not “erotic movies” with bimbos whose only talent is taking their clothes off.
The only one that comes to mind immediately where that is completely accurate is Inserts (1975). Jessica Harper and Veronica Cartwright are the only two women in the cast, and they both got naked, although Cartwright was the only one to do full-frontal nudity.
The Blue Lagoon is a tricky one. There is only one female character, but it was played by three different people (Brooke Shields, Kathy Troutt and a little girl playing the character at a younger age). It is fair to say that the only female character got naked (or at least topless) but it was not Brooke. It was Kathy Troutt, her body double.
In Utopia, every woman got naked except Charlotte Vega (darn it!), and that was quite a few women.
In Steaming, I think every woman got naked except Diana Dors.



