Millipedes (Class Diplopoda) are terrestrial arthropods that belong to the subphylum Myriapoda. There are probably as many as 80,000 millipede species worldwide (Sierwald & Bond, 2007), but around 12,000 have been described so far (Brewer et al., 2012), distributed in 16 orders and 145 families (Shelley, 2007). Of this astonishing diversity 9 orders, 48 families and well over 1,500 species are currently described from Europe (Kime & Enghoff, 2017). The family Polyzoniidae Newport, 1844, with 6 genera and 20 described species worldwide (Enghoff et al., 2015), is represented in Europe by three species of the genus Polyzonium Brandt, 1837, P. eburneum Verhoef, 1907, P. transsilvanicum Verhoeff, 1898 and P. germanicum Brandt, 1837. The first two mentioned species have a restricted distribution in central and Eastern Europe, respectively, while P. germanicum is widespread in most of the continent (Kime & Enghoff, 2011). Two main European populations (Fig. 1), one in the eastern half of Europe and one in the western half (including France and SE Britain), have been described for P. germanicum (see Kime & Enghoff, 2011). An area of central Europe, with only a few records of the species, seems to separate these two populations (Kime, 2001), but no morphological (Schubart, 1934) nor ecological (Kime & Enghoff, 2011) differences have been found between them. To date P. germanicum was not known in the Iberian Peninsula.

This report describes a population that has been found in the Gresolet forest (Fig. 1), located into the Cadí-Moixeró Natural Parc (Saldes municipality, Barcelona province, Spain). Ten specimens of P. germanicum were collected by the author (with collection permit inside the natural park) in two dates (14.xi.2008, 5 young specimens, and 14.v.2009, 2 ♀♀ and 3 ♂♂) from litter layer and under logs and stones in the beech forest at 1,300 m above sea level (position 42°15’32.5” N, 1°42’47.2” E). The five young specimens are preserved in absolute ethanol and deposited at the E. Mateos collection (Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Facultat de Biologia, Universitat de Barcelona). The five adult specimens (2 ♀♀ and 3 ♂♂) are preserved in 70% ethanol and deposited at the Centre de Recursos de Biodiversitat Animal (Facultat de Biologia, Universitat de Barcelona) with collection codes CRBA-92751 to CRBA-92755. The Gresolet beech forest represents the southernmost locality of the western European population of the species and the first record for the Iberian Peninsula. The forest is crossed by the Mulleres stream and is distributed in a range of altitudes between 1,000 and 2,000 m. The area is characterized by a continental climate with Mediterranean influence, with relatively high precipitation and soft temperatures. The Gresolet forest host a mosaic of plant communities including oak grove (Quercus pubescens Willd.), beech forest (of Fagus sylvatica L.), fir forest (of Abies alba Mill.) and pine forests (of Pinus sylvestris L. and Pinus mugo Turra).

Polyzonium germanicum is a distinctive rather slug-like millipede, some 5 to 18 mm in length, with a yellowish to orange brown body composed of 35–60 segments and a very small and characteristic triangular head (Fig. 2A); when curled into a spiral it is said to resemble beech bud scales (British Myriapod & Isopod Group, 2020; Enghoff et al., 2015). In P. germanicum (as in all Polyzoniida) males and females are externally very similar. Only the transformation of legs-9 and legs-10 into gonopods in males (in stadium IV) allows differentiating the sexes (Couret & David, 1985). Polyzonium germanicum is a liquid feeder species (Couret, 1985) and very hygrophilous in its habitat requirements (David, 1983). Forests with thick humus layers and high humidity levels around the year is the preferred habitat of the species (David & Vannier, 1995). These forests may be coniferous, mixed or deciduous, with dense, open or clearing structure, but always with wet (or even waterlogged) soils (see Kime & Enghoff, 2011). Characteristically P. germanicum females brood the eggs (Enghoff, 1984). They remain curled up around them until hatching, while secreting a repellent substance that probably also acts as a biocide preventing the rotting of the eggs (Minelli, 2015). A couple of specimens collected on 14.v.2009 were observed during mating activities (Fig. 2B), and one female deposited an egg mass on 16.vii.2009 (Figs. 2C–D).