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.

Keywords:

• freshwater mussel
• Iberian Peninsula
• taxonomy
• endemic
• conservation

Acknowledgements

We wish to thank the Instituto da Conservação da Natureza, Parque Natural do Vale do Guadiana, Junta de Comunidades de Castilla La Mancha and Junta de Andalucia for their support of sampling trips. Many gracious collectors provided us with samples from around the Iberian Peninsula. We also thank the Museu Nacional de História Natural of Lisbon for their assistance in experiments with fish hosts. Joaquim Teodósio provided valuable information about several populations in the Guadiana basin. Dr Karl-Otto Nagel provided valuable help and comments throughout the study about the morphological characters of Unio and also supplied Unio crassus specimens from various locations in Europe. We thank Rolanda Albuquerque de Matos and Phillipe Bouchet for helping us locate the types of U. tumidiformis and U. eupygus. Plates were compiled by J. Muñoz of the photography facility of the MNCN (Madrid, Spain). Dr Louise Allcock provided invaluable help to improve the manuscript. The author Joaquim Reis received a grant from the Fundação para a Ciência e Tecnologia (SFRH/BD/12687/2003) and two Synthesis grants (ES-TAF-1005 and FR-TAF-985) for studying the MNCN and MNHN collections.