Convergent evolution of shell shape in freshwater limpets: the African genus Burnupia

Convergent evolution of shell shape is a well known phenomenon in gastropods that has caused much confusion in taxonomic and systematic studies. A paradigm is the patelliform shell shape in several taxa of the order Basommatophora. Historically, most freshwater limpets were assigned to the family Ancylidae. Based on anatomical data, some taxa were subsequently moved to different families. However, there are still doubts about the monophyly of the remaining ancylids. This is also true for the African limpets and particularly for species of the genus Burnupia Walker, 1912. In the present paper, two independent molecular markers (COI, 18S rRNA) are used to (a) infer the position of Burnupia within the Basommatophora and (b) to test whether the shell shape of Burnupia evolved independently. Bayesian and maximum likelihood analyses of 12 genera of limnic Basommatophora indicate that Burnupia not only appears to be distinct from the Ancylidae, but also from all other representatives of the superfamily Planorboidea studied here. Based on a generally well-supported phylogeny and preliminary anatomical data, it is concluded that patelliform shell shapes evolved at least three times in the taxa studied here and that the shell shape of Burnupia represents another case of convergent evolution. Previously proposed functional and evolutionary scenarios for the evolution of patelliform shell and their relevance for freshwater limpets are discussed.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 577–586.