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]
           Clade neomura Cavalier-Smith, 1987
             Domain Eukaryota Chatton, 1925 - eukaryotes
               Clade discaria Cavalier-Smith, 2021
                 Clade dorsates Cavalier-Smith, 2021
                   Clade podiates Cavalier-Smith, 2012
                     [crown] Clade Amorphea Adl et al. 2012 [Simpson, Medina & Adl 2020]
                       [crown] Clade Obazoa Brown, Sharpe, Silberman, Heiss, Lang, Simpson & Roger 2013
                         [crown] Clade Opisthokonta Cavalier-Smith 1987 [Simpson & Medina 2020] - animal-fungal clade
                           Superkingdom Holozoa Lang, O'Kelly, Nerad, Gray & Burger, 2002
                             Clade filozoa Shalchian-Tabrizi, Minge, Espelund, Orr, Ruden, Jakobsen & Cavalier-Smith, 2008
                               Kingdom Animalia Linnaeus, 1758 - animals
                                 Clade Planulozoa Wallberg, Thollesson, Farris & Jondelius 2004
                                   [crown] Phylum Cnidaria Hatschek, 1888 [coordinate rank] - cnidarians
                                     [crown] Subphylum Medusozoa Petersen, 1979
                                       [crown] Class Hydrozoa Owen, 1843
                                         "A-forms"
                                           Order Anthoathecatae
                                             Suborder Capitata Kühn, 1913 () sensu stricto
                                               Family Hydridae Dana, 1846
                                                 Genus Hydraᵀ Linnaeus, 1758
                                                   Hydra americana L.H. Hyman, 1929
                                                   Hydra attenuata Pallas, 1766
                                                   Hydra canadensis Rowan, 1930
                                                   Hydra carnea L. Agassiz, 1850
                                                   Hydra circumcincta P. Schulze, 1914
                                                   Hydra graysoni Maxwell
                                                   Hydra littoralis L.H. Hyman, 1931
                                                   Hydra oligactis (Pallas, 1766)
                                                   Hydra oxycnida P. Schulze, 1914
                                                   Hydra utahensis L.H. Hyman, 1931
                                                   Hydra vulgaris Pallas, 1766