New insights into the molecular phylogeny of the swimming crabs of the genera Portunus Weber, 1795 and Achelous De Haan, 1833 (Brachyura: Portunidae) of the Americas

Earlier studies of swimming crabs (family Portunidae) in the Americas suggested polyphyly of Portunus Weber, 1795. Our previous molecular analyses provided evidence for a subdivision of the genus, resulting in a reassignment of nine species of Portunus and one species of Cronius Stimpson, 1860 into the resurrected genus Achelous De Haan, 1833. These previous data also suggested that at least two more clades of species could be separated from Portunus sensu stricto. Our sampling efforts provided 11 additional (of potentially 12) eastern Pacific species originally treated under Portunus, which we herewith included in a new molecular phylogenetic analysis based on sequences of the 16S rRNA gene. With these additions, we present molecular data of almost all American species of Portunus sensu lato and contextualize them within the family Portunidae. Our findings strongly corroborate previous conclusions about the polyphyletic nature of Portunus. Some of the newly included species fit well into the clade previously defined as Achelous, whereas others are clearly assignable to clades that remain to be named. While we acknowledge the absence of most of the Indo-West Pacific species in our analyses, we can on the basis of morphology hypothesize that some of these Indo-West Pacific species (and valid subgenera) should cluster within the here-established clades