Incongruence between molecular phylogeny and morphological classification in amphipod crustaceans: a case study of Antarctic lysianassoids

In the Southern Ocean, the superfamily Lysianassoidea is one of the most important amphipod groups, both in terms of species number and abundance. Dominant members of this superfamily are species belonging to the orchomenid genus complex. The first molecular phylogenetic analysis on Antarctic species of these orchomenid genera is presented here, providing a framework for a systematic revision of these taxa. The current classification of the orchomenid genera is mainly based on mouthpart morphology. The validity of these morphological characters was assessed by resolving the phylogenetic relationships using nuclear 28S rRNA and mitochondrial cytochrome oxidase subunit I sequences. The molecular data rejected most of the previously proposed taxonomic subdivisions within this complex. The genera Abyssorchomene and Orchomenella as well as the subgenus Orchomenopsis appeared to be non-monophyletic. This implies that the diagnostic characters in this group are likely a result of convergent evolution. Further, our results indicated the necessity of a revision of the family-level systematics.