Phylum [Mollusca] Linnaeus, 1758 - molluscs
   Class Gastropoda Cuvier, 1795 - snails and slugs
     Subclass Opisthobranchia Milne-Edwards, 1848 - opisthobranchs see Order Opisthobranchia Milne-Edwards, 1848
       Order Cephalaspidea Fischer, 1883
         Superfamily Acteonacea d'Orbigny, 1835 see Superfamily Acteonoidea d'Orbigny, 1843
           Family Aplustridae Gray, 1847
             Genus Hydatina Schumacher, 1817
               1 Subgenus Hydatina (Aplustrum) Schumacher, 1817 see Genus Aplustrum Schumacher, 1817
               2 Subgenus Hydatina (Hydatina) Schumacher, 1817 see Genus Hydatina Schumacher, 1817