Distribution and ecology of Mercuria tachoensis (Gastropoda: Hydrobiidae) in Portugal and evidence that M. edmundi is conspecific

Distribution and ecology of Mercuria in Portugal are reviewed. M. tachoensis was still found present over much of the range recorded historically in the lowlands of W. Portugal. Our recent records are almost all of it living in small streams with clean water close to spring-heads (26 of 28 localities), with none from the larger rivers in W. Portugal. However, a site in the R. Guadiana in Baixo Alentejo had living snails on mud exposed where fresh or slightly saline river water had fallen during low tides. Since its original description in 1986, M. edmundi has been differentiated from M. tachoensis only on the basis of larger shell size, presence of a large rounded bulge on the penial appendage and shorter penis relative to length of the appendage. We demonstrate that size of the penial appendage is correlated with shell size; both apparently increase seasonally from November to May. Also, intermediates are frequent, and there is no consistent correlation of penis length with development of the appendage. Hence it is inferred that the type material of M. edmundi was of M. tachoensis approaching sexual maturity, with shells approaching full size, so the name should be regarded as a taxonomic synonym of the latter