A molecular phylogeny of the patellid limpets (Gastropoda : Patellidae) and its implications for the origins of their antitropical distribution

The geographical distribution of the limpet family Patellidae is essentiall y antitropical, with 18 species in southern Africa, 10 in the northeastern Atlantic, and only 11 species elsewhere (although 4 of these do occur in th e tropics) One possible explanation for this distribution is the suggestion of a recent, perhaps Early Pliocene, migration from southern Africa northw ard. We tested this hypothesis by constructing a molecular phylogeny, deriv ed from partial sequences of the 125 and 16S mitochondrial genes, obtained from 34 of the 38 patellid species; Five species of Nacellidae and 3 of Lot tiidae were included as potential outgroups. Analysis revealed that two pat ellid clades are represented in the northeastern Atlantic. The typical Euro pean patellids (Patella sensu stricto) form a single clade within which the re is little molecular divergence, but are distant from all other patellids , thus refuting the idea of recent southern ancestry. From the limited foss il record and estimated rates of molecular divergence, we suggest that Pate lla s.s. may have originated at least as early as the Upper Cretaceous and that its northern distribution may have been achieved at the same time. The second patellid clade present in the northeastern Atlantic is the genus Cy mbula, of which the single species Cymbula safiana extends from West Africa to the Mediterranean. in contrast to Patella, s.s., C. safiana is indeed a member of an otherwise southern African clade and may have attained its pr esent distribution more recently, during the Miocene. The geographical orig in of the family remains unclear, but a Mesozoic radiation in southern Gond wana is possible. By optimizing morphological characters on our molecular t ree, we consider the evolution of shell mineralogy and sperm ultrastructure . We also discuss the phylogenetic classification of the patellids and pres ent some evidence that the family may not be monophyletic. (C) Academic Pre ss.