Phylogenetic relationships of superfamily Gammaroidea (Amphipoda) and its allies from Japan

The current superfamilial classification of suborder Gammaridea, at least of the Japanese members, requires a full reassessment of their phylogenetic relationships. We investigated 17 species representing six families in three superfamilies from Japan, based on partial sequences of the mitochondrial 16S rRNA and nuclear 28S rRNA genes. Members of superfamily Gammaroidea are characterized by having gammarid-type calceolus on their antennae, but our molecular analyses did not support the monophyly of Gammaroidea. The unique gammarid-type calceolus found in Gammaroidea may not be a synapomorphy for this group. Monophyly of the families studied, except for Melitidae, was supported by neighbor-joining, maximum parsimony, and maximum likelihood analyses. The molecular analyses revealed that during their evolutionary history, gammaroidean amphipods repeatedly switched between marine and freshwater habitats.