On becoming cemented: evolutionary relationships among the genera in the freshwater bivalve family Etheriidae (Bivalvia: Unionoida)

A robust phylogeny for the Unionoida is emerging and presumed relationships of some major clades are being questioned. The Etheriidae or freshwater oysters has been a distinct family for over 160 years and currently contains three cemented genera:Acostaea(Columbia, South America),Pseudomulleria(India) andEtheria(Africa and Madagascar). Starobogatov (1970,Nauka, 1–372), Mansur and da Silva (1990,Amazoniana,11(2), 147–166) and Bonetto (1997,Biociências,5, 113–142) present conflicting testable hypotheses regarding the evolution of these taxa. Using cytochrome c oxidase subunit I DNA sequences the evolutionary relationships of these three genera has been examined, by comparing them to representatives of 30 other unionoid taxa from around the world. These analyses placeAcostaeaandEtheriawithin the Mycetopodidae whilePseudomulleriafalls within the Unionidae. A monophyletic Etheriidae, composed of cemented freshwater bivalves, is not supported by the present analyses. Furthermore, the analyses indicate that cementation in the Unionida has evolved at least twice.