Unio tumidus, Retzius, 1788

Araujo, Rafael, Buckley, David, Nagel, Karl-Otto, García-Jiménez, Ricardo & Machordom, Annie, 2018, Species boundaries, geographic distribution and evolutionary history of the Western Palaearctic freshwater mussels Unio (Bivalvia: Unionidae), Zoological Journal of the Linnean Society 182 (2), pp. 275-299 : 280

The U. tumidus lineage

The U.tumidus lineage included samples from European rivers (namely, the Seine, Danube, Rhine, Thames and Weser), a Swedish lake, the Izorka and Kovash rivers in Russia and the Dnieper River in Ukraine ( Fig. 2 ). This species is absent from the Iberian Peninsula and North Africa. Samples from the Rhine and Thames rivers and Bjornsjon Lake ( Sweden) shared the same haplotype (Supporting Information, Fig. S3 ).

The species had an elongated shell with an anterior umbo, but a characteristic cuneiform posterior end with a descending dorsal posterior margin, which clearly distinguishes this taxon from the other species. Nevertheless, there were specimens with short shells that were very difficult to identify ( Fig. 3 ). We did not have access to the Ukrainian and Russian shells.

Figures

Figure 2. Schematic distribution of the Unio species in the Western Palaearctic. Points indicate the general vicinity of sampled localities. See Supporting Information, Table S1 for details.

Figure 3. Differing shell shapes of Unio tumidus. A, Franconian Saale, a tributary of the Main River (Rhine), Germany. B, Fulda River (Weser), Germany. C, Okna River (Danube), Slovakia. D, Danube River, Slovakia. E, Ferma Lake (Rhine), Germany. F, Thames River, UK. G, Fulda River (Weser), Germany. H, Rhine River, Germany. I, Horloff River (Rhine), Germany. Scale bar 2 cm.