[Kingdom] Animalia Linnaeus, 1758 - animals
   Grade Plastidozoa [monotypic]
     [Phylum] Protozoa (Goldfuss, 1818) C.T. von Siebold, 1854 see Kingdom Protozoa Goldfuss, 1818
       Grade Corticata Lankester, 1877
         Class Corticata Lankester, 1877 [monotypic]
           Order Gregarinidæ
             Genus Monocystis Stein, 1848