substage

sub- +‎ stage

substage (plural substages)

1. The stage, below the main stage of a microscope, to which attachments are fixed.
2. A stage making up part of a larger stage.
   • 1958, Division of Mines and Geology, Washington, Information circular

     Which, then, of these glacial substages provided the proper conditions and saw the first population of man in America?

   • 1991, Rusel DeMaria; Zach Meston, Nintendo Games Secrets, volume 2, page 324:

     These passwords will take you to every substage of the game.

• stage bus