Redescription of Unio tumidiformis Castro, 1885 (Bivalvia, Unionidae), an endemism from the south-western Iberian Peninsula

Abstract

The possible occurrence of Unio crassus Philipsson, 1788 on the Iberian Peninsula has been a controversial issue since the nineteenth century. Several characters, including molecular, morphological and life cycle, show that the Iberian taxon is related to, but well differentiated from, the central European U. crassus. The valid name for this Iberian taxon is Unio tumidiformis Castro, 1885. Live populations are distributed throughout the Guadiana, Mira and Sado river basins. Unio tumidiformis can be distinguished from other Unio species by its regular oval shape, high relative height and width, strong wavy umbonal rugae, supra-cardinal tooth on the right valve, and lower glochidium height. From the potential fish hosts tested, only Squalius alburnoides (Steindachner, 1866) resulted in juvenile drop-off, suggesting some degree of specialization in the parasite–host relationship. The endemic nature, population status and habitat of U. tumidiformis make this species important from a conservation point of view.