Phylum Mollusca Linnaeus, 1758 - molluscs Conchifera Gegenbaur, 1878 see Subphylum Conchifera Gegenbauer, 1878 Cyrtosoma Class Gastropoda Cuvier, 1795 - snails and slugs Subclass †Archaeobranchia Parkhaev, 2001 1 Order †Helcionelliformes Golikov & Starobogatov, 1975 1.n Order †Pelagielliformes Runnegar & Pojeta, 1985