Taxonomy, phylogeny and biogeography of Politolana Bruce, 1981 (Crustacea: Isopoda: Cirolanidae)

Abstract

A taxonomic revision of Politolana based on an inferred phylogeny of the genus is presented. Included are revised descriptions and diagnoses of the genus and species, and a key to all the known species. Six of the 10 previously described species are redescribed: Politolana polita (Stimpson, 1853), Politolana concharum (Stimpson, 1853), Politolana micropthalma (Hoek, 1882), Politolana impressa (Harger, 1883), Politolana eximia (Hansen, 1905) and Politolana wickstenaeWetzer et al., 1987. Neotypes are designated for P. polita and P. concharum, and lectotypes are designated for P. impressa and P. eximia. The diagnosis of the recently described Politolana tricarinata Riseman et al. (2001) is included and two new species, Politolana impostor and Politolana haneyi, are described. All descriptions include synonymies, distributional information and illustrations of all appendages, mouth parts and dorsal and lateral body views (with the exception of the P. wickstenae). A data matrix of 61 morphological characters for 15 taxa (10 previously described and two new Politolana species, and three out-group genera) was analysed using parsimony-based cladistic methods. The analysis resulted in five equally most parsimonious trees. The relationships among most Politolana species were fully resolved in the strict consensus tree and indicate that Politolana, as previously defined, is paraphyletic. We recommend that three species, Politolana crosnieriBruce (1996), Politolana obtusispina (Kensley, 1975) and Politolana dasyprionBruce (1991), be removed from the genus. New generic assignments for these species await publication of the phylogenetic analysis of the family Cirolanidae (currently being prepared by the second author). The phylogeny of Politolana comprises two well-supported species-group clades. Collection data indicate that Politolana species are benthic scavengers occurring on the continental shelf and slope from shallow waters to depths greater than 650 m. The geographical distribution of the genus, both at the species level and at deeper levels of the phylogeny, corresponds to recognized zoogeographical regions. The genus has had virtually all of its radiation in the west Atlantic. A single north-east Atlantic species (P. micropthalma), with its closest relative in the north-west Atlantic, is either the result of a dispersal event from the western Atlantic, or a vicariance by-product of the opening of the Atlantic. Evolution within the genus has established an antitropical distribution resulting in a south-west Atlantic clade. Politolana haneyi has a distribution that was established sometime before the closure of the Panama Seaway and that species was divided into Pacific and Gulf of Mexico populations with the formation of the Panamanian isthmus. A high degree of sympatry among sister species in the genus is also apparent. Potential historical explanations for these patterns are reviewed.