Phylum Mollusca Linnaeus, 1758 - molluscs Class Gastropoda Cuvier, 1795 - snails and slugs Subclass Prosobranchia Milne-Edwards, 1848 - prosobranchs see Class Gastropoda Cuvier, 1795 Superorder Archaeogastropoda Thiele, 1925 Order Vetigastropoda Salvini-Plawen, 1980 - archaeogastropods s.l. Superfamily Seguenzioidea Verrill, 1884 [monotypic] Family Seguenziidae Verrill, 1884 Genus Thelyssa Bayer, 1971