Phylogenetic relationships among western Atlantic representatives of Pilumnus Leach, 1816 (Decapoda, Brachyura, Pilumnidae) based on molecular markers, with comments on biogeography

<i>Pilumnus</i> is a highly speciose brachyuran crab genus distributed in tropical and temperate oceans. Previous systematic studies of the genus have revealed a high degree of uncertainty as to phylogenetic relationships. This is particularly evident among western Atlantic representatives, which have never been examined comprehensively from a phylogenetic perspective. A comparative molecular phylogenetic analysis of <i>Pilumnus</i> from the western Atlantic was conducted using mitochondrial sequences of the 16S rRNA and Cytochrome Oxidase subunit I genes. Sequences for 14 species from the western Atlantic were generated, included in the analyses, and compared to sequences of congeners from other biogeographic regions. Phylogenetic hypotheses including divergence time data were derived, genetic distances were calculated, and species delimitation methods were applied. Our results reveal that these taxa represent two distinct lineages that do not reflect modern geography in their distributions. The phylogenetic reconstruction identified two separate lineages presently treated under <i>P. reticulatus</i>, and species delimitation methods suggested that they may correspond to two separate species. Similarly, delimitation analyses indicated that an accessed specimen phylogenetically close to <i>P. lacteus</i> may represent an undescribed species. The results evince the importance of molecular phylogenetic studies in comprehending the evolutionary and biogeographic patterns that characterise the marine decapod biota.