Euthyneura is a taxonomic infraclass of snails and slugs, which includes species exclusively from marine, aquatic and terrestrial gastropod mollusks in the clade Heterobranchia.

Within this taxon, the Gastropoda have reached their peak in species richness and ecological diversity.

Marine Opisthobranchia, e.g., have evolved several clades specialised on less used food resources such as sponges or cnidarians.

Klussmann-Kolb et al. (2008) traced an evolutionary scenario regarding colonisation of different habitats based on phylogenetic hypothesis and they showed that traditional classification of Euthyneura needs to be reconsidered.

[3] Jörger et al. (2010)[7] have redefined major groups within the Heterobranchia and a cladogram showing phylogenic relations of Euthyneura is as follows:[7] Lower Heterobranchia (including Acteonoidea) - Lower Heterobranchia does not form a clade in the study by Jörger et al. (2010):[7] Nudipleura Euopisthobranchia Panpulmonata Cladogram showing phylogenic relations of Euthyneura sensu Wägele et al. (2014):[8][2] Lower Heterobranchia Rissoelloidea Acteonoidea Pleurobranchoidea Anthobranchia Cladobranchia Euopisthobranchia Panpulmonata Kano et al. (2016) proposed a new taxon Ringipleura and classified Ringiculoidea as sister group to Nudipleura:[2] Lower Heterobranchia Rissoelloidea Acteonoidea Ringiculoidea Nudipleura Euopisthobranchia Panpulmonata