fossil marine animal genera Linnaeus, 1758 - animals
   Phylum Cnidaria Hatschek, 1888 - cnidarians
     Class Hydrozoa Owen, 1843
       1 Order Trachylinida see Order Trachylina Haeckel, 1879
       2 Order Hydroida Johnston, 1836 - hydroids see Order Anthoathecatae
       3 Order Siphonophorida Eschscholtz, 1829 see Order Siphonophora Eschscholtz, 1829
       4 Order Milleporina - millepore hydrocorals see Suborder Capitata Kühn, 1913 () sensu stricto
       5 Order Stylasterina - stylasterine hydrocorals see Suborder Filifera Kühn, 1913
       6 Order Lemniscaterina Gallitelli, 1979
       7 Order †Sphaeractinida
       8 Order †uncertain