The Patellogastropoda, common name true limpets and historically called the Docoglossa, are members of a major phylogenetic group of marine gastropods, treated by experts either as a clade or as a taxonomic order. The clade Patellogastropoda is deemed monophyletic based on phylogenetic analysis. Taxonomy Patellogastropoda was proposed by David R. Lindberg, 1986, as an order, and was later included in the subclass Eogastropoda Ponder & Lindberg, 1996. 2005 taxonomy Bouchet & Rocroi, 2005 designated Patellogastropoda, true limpets, as a clade, rather than as a taxon, but within included superfamilies and families as listed below. Families that are exclusively fossil are indicated with a dagger †: Superfamily Patelloidea Family Patellidae Superfamily Nacelloidea Family Nacellidae Superfamily Lottioidea Family Lottiidae Family Acmaeidae Forbes, 1850 subfamily Acmaeinae Forbes, 1850 subfamily Pectinodontinae Pilsbry, 1891 subfamily Rhodopetalinae Lindberg, 1981 Family Lepetidae Superfamily Neolepetopsoidea Family Neolepetopsidae † Family Daminilidae † Family Lepetopsidae With the exception of calling Patellogastropoda a clade rather than an order, as was previously the case in Ponder and Lindberg, 1997 the taxon has not changed much, differing more in the arrangement of its content rather than in the overall composition. Bouchet and Rocroi omitted Ponder and Lindberg's suborders, and added in the superfamily Neolepetopsoidea. 2007 taxonomy Nakano & Ozawa (2007) made many changes in the taxonomy of the Patellogastropoda, based on molecular phylogeny research: Acmaeidae is a synonym of Lottiidae; Pectinodontinae is elevated to Pectinodontidae; new family Eoacmaeidae with the new type genus Eoacmaea is established. A cladogram based on sequences of mitochondrial 12S ribosomal RNA, 16S ribosomal RNA and cytochrome-c oxidase I (COI) genes showing phylogenic relations of Patellogastropoda by Nakano & Ozawa (2007) and superfamilies based on World Register of Marine Species: Note that the family Neolepetopsidae is not in the cladogram above, because its members were not genetically analyzed by Nakano & Ozawa (2007). However, two Neolepetosidae species Eulepetopsis vitrea and Paralepetopsis floridensis were previously analyzed by Harasewych & McArthur (2000), who confirmed their placement within Acmaeoidea/Lottioidea based on analysis of partial 18S rDNA. The Daminilidae and Lepetopsidae are also not included in the cladogram, because they are exclusively fossil families. All of these three families belong to superfamily Lottioidea. Actual taxonomy based on data by Nakano & Ozawa (2007) with placement of the three remaining families (Neolepetopsidae, Daminilidae, Lepetopsidae) into Lottioidea is like this: superfamily Eoacmaeoidea family Eoacmaeidae superfamily Patelloidea family Patellidae superfamily Lottioidea family Nacellidae family Lepetidae family