living organisms see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Superkingdom Eukaryotae see Domain Eukaryota Chatton, 1925
     Kingdom Animalia Linnaeus, 1758 - animals
       Subkingdom Eumetazoa Butschli, 1910 see [unranked] Eumetazoa Bütschli, 1910
         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
                 01 Family Acteonidae d'Orbigny, 1843, nom. protect. - bubble shells
                 02 Family Ringiculidae Philippi, 1853
                 03 Family Hydatinidae Pilsbry, 1895, nom. illeg. see Family Aplustridae Gray, 1847
                 04 Family Bullinidae Gray, 1850
                 05 Family Scaphandridae Sars, 1878 see Family Cylichnidae Adams & Adams, 1854
                 06 Family Philinidae Gray, 1850 (1815)
                 07 Family Aglajidae Pilsbry, 1895 (1847)
                 08 Family Gastropteridae Swainson, 1840
                 09 Family Diaphanidae Odhner, 1914 (1857)
                 10 Family Notodiaphanidae Thiele, 1931
                 11 Family Bullidae Gray, 1827
                 12 Family Atyidae Thiele, 1925, orth. rej. see Family Atydidae Thiele, 1925
                 13 Family Retusidae Thiele, 1925