Bigyra Cavalier-Smith, 1998
   Subphylum Opalozoa Cavalier-Smith, 1992
     Infraphylum Placidozoa Cavalier-Smith, 2013
       Superclass Opalinata Wenyon, 1926
         Class Opalinea Wenyon, 1926
           Order Opalinida Poche, 1913
             1 Family Karotomorphidae Travis, 1934 [monotypic]
             2 Family Opalinidae Claus, 1874