Hidden in plain sight: six millipede species (Myriapoda: Diplopoda) new for the fauna of Switzerland

Diplopoda are poorly studied in many regions. The last comprehensive work on the millipede fauna of Switzerland was published in 1993 and listed 124 outdoor-living species. Recent sampling efforts have resulted in the discovery of six millipede species of European origin that were not previously known to occur in Switzerland: Cylindroiulus britannicus (Verhoeff, 1891), C. salicivorus Verhoeff, 1908, C. vulnerarius (Berlese, 1888), Heteroiulus intermedius (Brölemann, 1892), Anamastigona pulchella (Silvestri, 1894) and Macrosternodesmus palicola Brölemann, 1908. None of them is currently invasive in Switzerland, but some are rapidly expanding across Europe and other regions of the world. A species which was previously only known from northern Italy, H. intermedius, was found in a forest close to Bellinzona. It is likely a native Swiss species which has previously been overlooked. The other five species were collected in human-made habitats in the city of Basel and its surroundings, suggesting human-caused introduction. Two species, C. britannicus and M. palicola, likely have an Atlantic origin, while the three remaining species, C. salicivorus, C. vulnerarius and A. pulchella, are originally from Italy. The biogeography of these six species is discussed, and photographs of specimens of each species and their gonopods are presented.