Phylum Mollusca Linnaeus, 1758 - molluscs
   Class Gastropoda Cuvier, 1795 - snails and slugs
     Subclass Opisthobranchia Milne-Edwards, 1848 - opisthobranchs see Order Opisthobranchia Milne-Edwards, 1848
       1 Order Cephalaspidea Fischer, 1883
       2 Order Acochlidioidea Küthe, 1935 [monotypic] see Order Acochlidia Odhner, 1937
       3 Order Sacoglossa Ihering, 1876 - sacoglossans
       4 Order Anaspidea Fischer, 1883 - sea hares
       5 Order Notaspidea Fischer, 1883 [monotypic] see Suborder Notaspidea Fischer, 1883
       6 Order Thecosomata Blainville, 1824 [monotypic] - shelled pteropods see Suborder Thecosomata Blainville, 1824
       7 Order Gymnosomata Blainville, 1824 - naked pteropods see Suborder Gymnosomata Blainville, 1824
       8 Order Nudibranchia Cuvier, 1814 - "true" nudibranchs