Phylogenetic analysis of mitochondrial LSU rRNA in oniscids.

The phylogenetic relationships among oniscids (Crustacea, Isodopa) remain contradictory despite numerous morphological studies. We have investigated them using molecular data. Partial sequences of the mitochondrial LSU rRNA gene were obtained from 42 species of aquatic and terrestrial crustaceans from 31 genera. This gene provided well-supported information, notwithstanding the high taxonomic level of this study, indicating a useful amount of variation despite the noise due to multiple substitutions. The phylogenetic inferences demonstrated that a) Crinocheta and Synocheta sections are monophyletic and sister-groups, b) Ligiidae and Tylidae representatives are in a basal position compared to other oniscids, c) Helleria brevicornis, the only representative of the Helleriinae subfamily, has undergone different evolution, d) the relationships between aquatic isopods and ancient groups of Oniscidea are not resolved, probably due to fast radiation not discriminated by the molecular phylogeny.