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 Gymnosomata Blainville, 1824 - naked pteropods see Suborder Gymnosomata Blainville, 1824
         1 Family Pneumodermatidae Latreille, 1825
         2 Family Notobranchaeidae Pelseneer, 1886
         3 Family Cliopsidae Costa, 1873 [monotypic]
         4 Family Clionidae Rafinesque, 1815
         5 Family Thliptodontidae Kwietniewski, 1902 (1902) see Subfamily Thliptodontinae Kwietniewski, 1902 (1902)
         6 Family Hydromylidae Pruvot-Fol, 1942 (1862) [monotypic]
         7 Family Laginiopsidae Pruvot-Fol, 1922 [monotypic]