Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         [crown] Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
           ?"viruses"
             Order Ortervirales
               Family Retroviridae
                 Subfamily Orthoretrovirinae
                   Genus Alpharetrovirus
                     1 Avian carcinoma Mill Hill virus 2
                     2 Avian leukosis virusᵀ
                     3 Avian myeloblastosis virus
                     4 Avian myelocytomatosis virus 29
                     5 Avian sarcoma virus CT10
                     6 Fujinami sarcoma virus
                     7 Rous sarcoma virus
                     8 UR2 sarcoma virus
                     9 Y73 sarcoma virus