ABSTRACT

As currently recognized by most taxonomists, the genus Cronius Stimpson, 1860, encompasses only two species, both distributed in tropical and subtropical waters. Cronius ruber (Lamarck, 1818) is reported from both the Pacific and Atlantic American coastlines, as well as the eastern Atlantic, and C. tumidulus (Stimpson, 1871) is reported to occur exclusively in the tropical western Atlantic. We examine potential differences between allopatric populations assigned to C. ruber, test hypothesized monophyly of the genus, and resolve the phylogenetic position of its members within the Portunidae. In so doing, we also revisit taxonomic classification of American species currently assigned to the genus Portunus. New 16S mtDNA sequences were obtained from representatives of the genera Charybdis, Cronius, Lupella, Lupocyclus, Polybius, Portunus, and Thalamita for examination along with sequences from GenBank. Slight but consistent genetic differences were found among populations assigned to Cronius ruber from the Pacific American coastline, the Atlantic American coastline, and the eastern Atlantic coastline (West Africa). The name C. edwardsii (Lockington, 1877) is resurrected for specimens from the eastern Pacific, but further analyses are needed to determine if additional taxonomic revisions may be required to more narrowly restrict use of the name C. ruber among a complex of Atlantic populations. Presently assigned members of Cronius do not form a monophyletic group. The well-defined clade representing C. ruber (including the resurrected C. edwardsii) is placed in a weakly supported grouping with representatives of Laleonectes, Thalamita, and Charybdis. In contrast, Cronius tumidulus forms a well-supported cluster with several present American representatives of the genus Portunus, which themselves are well separated from P. pelagicus, type species of that genus. Thus, we propose a revised taxonomy with placement of C. tumidulus in the resurrected genus Achelous De Haan 1833, an assignment that we also propose for nine American species currently treated under Portunus.