A CLADISTIC PHYLOGENY OF THE FAMILY PATELLIDAE (MOLLUSCA, GASTROPODA)

A phylogenetic hypothesis for the patellid limpets is reconstructed by cladistic analysis of morphological characters from 37 species, repre senting all but one of the living members of the family. Characters in cluded in the analysis are derived from shell shape and microstructure , headfoot and pallial complex, radula and sperm. The species fall int o four clades, providing the basis for a new phylogenetic classificati on into four monophyletic genera: Helcion (four species; southern Afri ca), Cymbula (eight species; southern Africa, eastern Atlantic, southe rn Indian Ocean), Scutellastra (17 species; southern and southwestern Africa, Australia, Indo-West Pacific, Eastern Pacific) and Patella (ni ne species; northeastern Atlantic and Mediterranean). The analysis sug gests sister-group relationships between Helcion and Cymbula, and betw een Scutellastra and Patella. In combination with present-day patterns of geographical distribution, this phylogenetic hypothesis is used to discuss the historical biogeography of the Patellidae. Scutellastra m ay have originated in southern Africa and dispersed across the Pacific , or alternatively may be a primitively Tethyan group. Both Helcion an d Cymbula appear to have originated in southern Africa, but three Cymb ula species have dispersed respectively to northwest Africa, St Helena and the southern Indian Ocean. The patellids of the northeastern Atla ntic form a single clade, Patella (including P. pellucida), which may have arrived by northward dispersal of an ancestor from southern Afric a, or possibly by vicariance of a widespread ancestral Tethyan distrib ution. The known fossil record of patellids is tao fragmentary to perm it choice between these alternatives.