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
         Superfamily Bulloidea Gray, 1827
           Family Retusidae Thiele, 1925
             1 Genus Retusa Brown, 1827
             2 Genus Cylichnina Monterosato, 1884
             3 Genus Pyrunculus Pilsbry, 1895
             4 Genus Relichna Rudman, 1971
             5 Genus Volvulella Newton, 1891