Bigyra Cavalier-Smith, 1998
   Subphylum Opalozoa Cavalier-Smith, 1992
     Infraphylum Placidozoa Cavalier-Smith, 2013
       Superclass Opalinata Wenyon, 1926
         Class Opalinea Wenyon, 1926
           Order Proteromonadida Grassé, 1952 [monotypic]
             1 Family Proteromonadidae Grassé, 1952 [monotypic]