Polydesmid millipedes in the MSS of the northern Iberian Peninsula (Diplopoda, Polydesmida, Polydesmidae)

The Superficial Subterranean Environment, known as the MSS (Milieu Souterrain Superficiel), was sampled at 15 localities of three main mountain systems in the northern Iberian Peninsula, at different time intervals from 2012 to 2021. A total of 2673 polydesmid individuals (Diplopoda: Polydesmida) were captured, of which 1970 could be identified with certainty as belonging to six species. The new records of these six species provide important new information about their distribution. Polydesmus angustus Latzel, 1884 is confirmed to inhabit the Atlantic region of the Iberian Peninsula. Archipolydesmus osellai Ceuca, 1968 is found for the third time since its description, but in the Iberian System far from its type locality in the Pyrenees. We provide new records of the rare millipede Polydesmus asturiensis Djursvoll, 2019 and slightly expand its known range. The known distribution of the Polydesmus racovitzai Brolemann, 1910 previously known from the Pyrenees and the Basque Mountains, is also extended to the Iberian System. The common and widely distributed in western Europe Polydesmus coriaceus Porat, 1870 and Propolydesmus dismilus (Berlese, 1891) are also recorded, but only the first one was abundant in the MSS. We also include photographs of the habitus and gonopods of the species found, as well as illustrations of the sampling methodology and habitats. The results highlight the importance of surveying the MSS in different mountain regions in order to increase knowledge about the biology and distribution of species.