Kingdom Animalia Linnaeus, 1758 - animals
   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 Acochlidioidea Küthe, 1935 see Order Acochlidia Odhner, 1937
         2 Order Cephalaspidea Fischer, 1883
         3 Order Runcinoidea Adams & Adams, 1854 see Suborder Cephalaspidea Fischer, 1883
         4 Order Sacoglossa Ihering, 1876 - sacoglossans
         5 Order Anaspidea Fischer, 1883 - sea hares
         6 Order Thecosomata Blainville, 1824 - shelled pteropods see Suborder Thecosomata Blainville, 1824
         7 Order Gymnosomata Blainville, 1824 - naked pteropods see Suborder Gymnosomata Blainville, 1824
         8 Order Notaspidea Fischer, 1883 see Suborder Notaspidea Fischer, 1883
         9 Order Nudibranchia Cuvier, 1814 - "true" nudibranchs