Kingdom Protoctista Hogg, 1860
   Phylum Rhizopoda Dujardin, 1835 - rhizopods see Phylum Cercozoa Cavalier-Smith, 1998
     Class Lobosea (Carpenter, 1861) Cavalier-Smith, 1993 see Subphylum Lobosa Carpenter, 1861
       Subclass Gymnamoebia (Haeckel, 1862) Cavalier-Smith, 1993 see [unranked] Gymnamoebae
         Order Amoebida - naked lobosid amebas see Class Amoebaea
           Genus Pneumocystis P. Delanoë & Delanoë (1912), incertae sedis