Clade Gymnosomata Clade Aplysiomorpha Group Acochlidiacea Clade Sacoglossa Group Cylindrobullida Clade Umbraculida Clade Nudipleura Clade Pleurobranchomorpha Clade Nudibranchia Clade Euctenidiacea Clade Dexiarchia Clade Pseudoeuctenidiacea Clade Cladobranchia Clade Euarminida Clade Dendronotida Clade Aeolidida Informal group Pulmonata Informal group Basommatophora Clade Eupulmonata Clade Systellommatophora Clade Stylommatophora Clade Elasmognatha Clade Orthurethra Informal group Sigmurethra Taxonomy In the following, more detailed list, indentation is used only for the ranks of superfamily and family. The clade names are not indented, but their hierarchy is indicated by the size of the font used. A clearer sense of the hierarchy of the clades can be drawn from the list immediately above this one. Paleozoic molluscs of uncertain systematic position (Existing as fossils only) Uncertain position (Gastropoda or Monoplacophora) unassigned to superfamily † Khairkhaniidae † Ladamarekiidae † Metoptomatidae † Patelliconidae † Protoconchoididae Archinacelloidea † Archinacellidae † Archaeopragidae Pelagielloidea † Pelagiellidae † Aldanellidae Scenelloidea † Scenellidae † Coreospiridae † Igarkiellidae Yochelcionelloidea † Yochelcionellidae † Stenothecidae † Trenellidae With isostrophically coiled shells of uncertain position (Gastropoda or Monoplacophora) † Bucanellidae † Bucaniidae † Euphemitidae † Pterothecidae † Sinuitidae † Tremanotidae † Tropidodiscidae With anisostrophically coiled shells of uncertain position (Gastropoda?) Euomphaloidea † Euomphalidae † Helicotomidae † Lesueurillidae † Omphalocirridae † Omphalotrochidae Macluritoidea † Macluritidae Basal taxa that are certainly Gastropoda (existing as fossils only) unassigned to superfamily † Anomphalidae † Codonocheilidae † Crassimarginatidae † Holopeidae † Isospiridae † Opisthonematidae † Paraturbinidae † Planitrochidae † Pragoserpulinidae † Pseudophoridae † Raphistomatidae † Rhytidopilidae † Scoliostomatidae † Sinuopeidae Clisospiroidea † Clisospiridae † Onychochilidae Loxonematoidea † Loxonematidae † Palaeozygopleuridae Ophiletoidea † Ophiletidae Straparollinoidea † Straparollinidae Trochonematoidea † Trochonematidae † Lophospiridae Clade Patellogastropoda Superfamily Patelloidea Family Patellidae Superfamily Nacelloidea Family Nacellidae Superfamily Lottioidea Family Lottiidae Family Acmaeidae Family Lepetidae Superfamily Neolepetopsoidea Family Neolepetopsidae † Family Daminilidae † Family Lepetopsidae Clade Vetigastropoda Not assigned to a superfamily: Family Ataphridae Family Pendromidae † Family Schizogoniidae Superfamily †Amberleyoidea † Family Amberleyidae † Family Nododelphinulidae Superfamily †Eotomarioidea † Family Eotomariidae † Family Gosseletinidae † Family Luciellidae † Family Phanerotrematidae Superfamily Fissurelloidea Family Fissurellidae Superfamily Haliotoidea Family Haliotidae † Family Temnotropidae Superfamily Lepetelloidea Family Lepetellidae Family Addisoniidae Family Bathyphytophilidae Family Caymanabyssiidae Family Cocculinellidae Family Osteopeltidae Family Pseudococculinidae Family Pyropeltidae Superfamily Lepetodriloidea Family Lepetodrilidae Family Clypeosectidae Family Sutilizonidae Superfamily †Murchisonioidea † Family Murchisoniidae † Family Cheeneetnukiidae † Family Hormotomidae Superfamily Neomphaloidea: subsequent research has placed this superfamily in its own clade, the Neomphalina, basal to the Vetigastropoda Family Neomphalidae Family Melanodrymiidae