Phylogenetic analysis of Euthyneura (Gastropoda) by means of the 16S rRNA gene: use of a 'fast' gene for 'higher-level' phylogenies

The phylogeny of Euthyneura is analysed by using DNA sequences of the mitoc hondrial 16S rRNA gene. Despite the common notion that this gene is too var iable to provide useful information at high taxonomic levels, such as in th e present study, bootstrap proportions are high for several clades in the s tudy. This indicates that there is a useful amount of variation despite the noise due to multiple substitutions. The analyses furthermore indicate tha t (i) Gymnosomata (represented by Clione) is not a part of Euthyneura, but Clione forms a clade with the caenogastropods; (ii) Acteon is the sister gr oup to the remaining euthyneuran taxa in the study; (iii) the nudibranch ta xa form two clades, one comprising Dendronotoidea, Arminoidea and Aeolidoid ea (together Cladobranchia) with Notaspidea (represented by Berthella) as s ister group, while the fourth nudibranch taxon, Doridoidea, forms a separat e clade; (iv) Cephalaspidea sensu stricto and Anaspidea form clades that ar e each other's sister groups (together Pleurocoela). Finally, there is no c lade present in the analyses corresponding to the taxon Opisthobranchia in the traditional sense, and the use of this name is probably better abandone d altogether.