Kingdom Animalia Linnaeus, 1758 - animals
   Phylum Cnidaria Hatschek, 1888 - cnidarians
     Class Hydrozoa Owen, 1843
       Genus †Drevotella Nitecki & Richardson, 1972
       ?Genus †Eoporpita Wade, 1972
       Genus Hydra Linnaeus, 1758
       1 Order Trachylinida see Order Trachylina Haeckel, 1879
       2 Order Hydroida Johnston, 1836 - hydroids see Order Anthoathecatae
       3 Order Milleporina - millepore hydrocorals see Suborder Capitata Kühn, 1913 () sensu stricto
       4 Order Stylasterina - stylasterine hydrocorals see Suborder Filifera Kühn, 1913
       5 Order Siphonophorida Eschscholtz, 1829 see Order Siphonophora Eschscholtz, 1829