The taxonomy of the Gastropoda as it was revised in 2005 by Philippe Bouchet and Jean-Pierre Rocroi is a system for the scientific classification of gastropod mollusks. (Gastropods are a taxonomic class of animals which consists of snails and slugs of every kind, from the land, from freshwater, and from saltwater.) The paper setting out this taxonomy was published in the journal Malacologia. The system encompasses both living and extinct groups, as well as some fossils whose classification as gastropods is uncertain. The Bouchet & Rocroi system was the first complete gastropod taxonomy that primarily employed the concept of clades, and was derived from research on molecular phylogenetics; in this context a clade is a "natural grouping" of organisms based upon a statistical cluster analysis. In contrast, most of the previous overall taxonomic schemes for gastropods relied on morphological features to classify these animals, and used taxon ranks such as order, superorder and suborder, which are typical of classifications that are still inspired by Linnaean taxonomy. In the Bouchet & Rocroi taxonomy, clades are used between the rank of class and the rank of superfamily. The clades are unranked. Bouchet and Rocroi use six main clades: Patellogastropoda, Vetigastropoda, Cocculiniformia, Neritimorpha, Caenogastropoda, and Heterobranchia. The first three of these major clades have no nesting clades within them: the taxonomy goes immediately to the superfamily level. Within the Caenogastropoda there is one extra clade. In contrast, within the Heterobranchia, for some of the nudibranch groups there are six separate clades above the level of superfamily, and in the case of most of the land snails, there are four clades above the level of superfamily. In some parts of the taxonomy, instead of "clade", Bouchet and Rocroi labelled groupings of taxa as a "group" or an "informal group". A clade must by definition contain only one lineage, and it was considered to be the case that these "informal groups" may either contain more than one lineage, or only contain part of a lineage. Further research will eventually resolve these questions. Since the publication of this taxonomic system in 2005, various proposals for changes have been published by other authors, for more information see changes in the taxonomy of gastropods since 2005. In 2017 this taxonomy was superseded by a revised taxonomy "Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families" by Philippe Bouchet & Jean-Pierre Rocroi, Bernhard Hausdorf, Andrzej Kaim, Yasunori Kano,