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 Gammaretrovirus
                     1 Viper retrovirus
                     2.1 Chick syncytial virus
                     2.2 Reticuloendotheliosis virus
                     2.3 Trager duck spleen necrosis virus
                     3.1.1 Murine leukemia virusᵀ
                     3.1.2? Guinea pig type-C oncovirus
                     3.2.1? Feline leukemia virus
                     3.2.2.1 Porcine type-C oncovirus
                     3.2.2.2.1 Koala retrovirus
                     3.2.2.2.2.1 Gibbon ape leukemia virus
                     3.2.2.2.2.2.1 Woolly monkey sarcoma virus
                     3.2.2.2.2.2.2? Finkel-Biskis-Jinkins murine sarcoma virus
                     3.2.2.2.2.2.3? Harvey murine sarcoma virus
                     3.2.2.2.2.2.4? Kirsten murine sarcoma virus
                     3.2.2.2.2.2.5? Moloney murine sarcoma virus
                     3.2.2.2.2.2.6? Gardner-Arnstein feline sarcoma virus
                     3.2.2.2.2.2.7? Hardy-Zuckerman feline sarcoma virus
                     3.2.2.2.2.2.8? Snyder-Theilen feline sarcoma virus