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 Acochlidioidea Küthe, 1935 see Order Acochlidia Odhner, 1937
       Order Anaspidea Fischer, 1883 - sea hares
       Order Aplysiomorpha Pelseneer, 1906 see Order Anaspidea Fischer, 1883
       Order Cephalaspidea Fischer, 1883
       Order Gymnosomata Blainville, 1824 - naked pteropods see Suborder Gymnosomata Blainville, 1824
       Order Notaspidea Fischer, 1883 see Suborder Notaspidea Fischer, 1883
       Order Nudibranchia Cuvier, 1814 - "true" nudibranchs
       Order Sacoglossa Ihering, 1876 - sacoglossans
       Order Thecosomata Blainville, 1824 - shelled pteropods see Suborder Thecosomata Blainville, 1824