Five new species are described, Plusiocampa (Didymocampa) cvijici Sendra & Antić, sp. nov., Plusiocampa (Plusiocampa) atom Sendra & Antić, sp. nov., Plusiocampa (Stygiocampa) barethae Sendra & Rađa, sp. nov., Plusiocampa (Stygiocampa) dulcici Sendra & Rađa, sp. nov. and Plusiocampa (Venetocampa) pirnati Sendra & Borko, sp. nov. This brings the number of cave-adapted species of campodeids known from the Dinarides, Eastern Alps, Balkan System and Rodope Massif to 28 (one species in the genus Campodea and 27 in Plusiocampa). Among Plusiocampa, four out of five subgenera are present (Pentachaetocampa is not present in the region studied): Didymocampa (one species), Plusiocampa s. str. (15 species), Stygiocampa (eight species) and Venetocampa (three species), whereby Stygiocampa and Venetocampa are endemic to the studied region. These results reveal the importance of the Dinarides karst region as a centre of diversification for campodeids and for cave animals in general. A monophyletic subgroup, consisting of Stygiocampa, Venetocampa and Plusiocampa s. str. and characterized by the absence of medial posterior thoracic macrosetae, presumably colonized the Dinaric plate during the middle of the Cenozoic and occurs in that area since then.
The order Diplura encompasses ten families with 1009 species, of which the Campodeidae and the Japygidae are the most diversified, comprising 85% of the total diversity (Koch, 2009; Sendra et al., 2021). Diplurans live in cryptic hypogean habitats all over the world, except for the polar circles and regions with permafrost soils (Condé, 1956; Sendra et al., 2021). They have successfully colonized cave ecosystems, particularly so the family Campodeidae, which encompasses 144 cave-adapted species that represent 30% of the total family diversity (Sendra et al., 2020a, b). Seventy percent of cave-adapted Campodeidae are distributed in European and Mediterranean karst regions (Sendra et al., 2020a). Prior to our study, 22 obligate cave-dwelling campodeid species were known from the Dinarides and adjacent karst regions, from the Eastern Alps to the Balkan System, and the Rhodope Massif (Sendra et al., 2020a). The number of cave-restricted species of different taxa is exceptionally high in the Dinarides and this region has been recognized as one of the world's major hotspot of subterranean biodiversity (Culver et al., 2006; Sket et al., 2004; Sket, 2012; Zagmajster et al., 2014; Antić & Makarov, 2019). Two campodeid genera inhabit the studied region: Campodea Westwood, 1842 and Plusiocampa Silvestri, 1912, with one endemic subgenus Stygiocampa Silvestri, 1934 (Bareth & Condé, 2001; Condé & Bareth, 1996; Sendra et al., 2020a).
The study of cave-adapted campodeids in the Dinaric and adjacent karst regions has a long history, starting with Joseph (1882) who described the troglomorphic species Campodea nivea Joseph, 1882 from the Jama v Košanskih Grižah Cave near Pivka (Slovenia). The species description encompasses only a short diagnosis, as it is the case with many other species described during this period (Sendra et al., 2020b). Denis (1923) and later Silvestri (1934, 1947) redescribed C. nivea in detail and proposed a new combination (Silvetri, 1934): Plusiocampa (Stygiocampa) nivea (Joseph, 1882). Further research revealed 11 new cave-adapted Plusiocampa species throughout the western Balkans: four in the subgenus Stygiocampa and seven in the subgenus Plusiocampa (Condé, 1947, 1948, 1950, 1959; Silvestri, 1931; 1933a, b). Ten new descriptions of cave-adapted campodeids followed at the end of the 20th and the beginning of the 21st century (Bareth, 1988; Bareth & Condé, 1984, 2001; Condé, 1974; Condé & Bareth, 1996; Neuhertz, 1984). Recently, Sendra et al. (2020a) revealed more than two hundred records of 22 cave-adapted campodeids species throughout the study area, identifying this region as a possible centre of campodeid diversification in caves, along with other well-sampled and rich regions as the Pyrenees and Cantabria (Sendra et al., 2020a, b). Recently collected diplurans from caves in the Dinarides and adjacent regions point to an overlooked diversity hotspot in that region. In the present paper we describe five new species from 15 caves and give additional biogeographic data on cave-adapted campodeids of the region.
MATERIAL AND METHODS
The specimens stored in ethanol 70-75% were washed using distilled water, mounted on microscope slides in Marc André II solution, and examined under a phase-contrast optical compound microscope (Leica DMLS). The illustrations were made with a drawing tube, while measurements were taken with an ocular micrometer. To measure body length, the specimens were mounted in toto and measured from the base of the distal macrochaetae of the frontal process to the supra-anal valve of the abdomen. Several specimens were coated with palladium-gold and used for SEM (Hitachi S-4100) photography and measurement of the sensilla.
The morphological descriptions and a