Sardinia, a hotspot of diversity for subterranean terrestrial isopods (Crustacea, Oniscidea)

Sardinia is a western Mediterranean island with a very large number of terrestrial isopods. Investigations in recent years have increased the number of Oniscidea known from the island to 115. Many of these species (40, of which 39 are endemic and 19 new to science) occur in subterranean environments, either in caves or in endogean habitats. They belong to the families Trichoniscidae (25 spp., 11 spp. nov.), Styloniscidae (1 sp.), Agnaridae (1 sp.), Cylisticidae (1 sp.), Porcellionidae (1 sp. nov.), and Armadillidiidae (11 spp., 7 spp. nov.). This high number is certainly due to the large extension of karst areas in the whole island with over 3,500 caves presently known. Twenty-three species are troglobiotic, three stygobiotic and 12 endogean, some of which occasionally occurring also in caves. Most of the species in the family Trichoniscidae are Tyrrhenian elements belonging to the genera Catalauniscus, Oritoniscus, Nesiotoniscus and Scotoniscus, which demonstrate the faunistic affinities of Sardinia with the north-eastern Iberian Peninsula and southern France, to which Sardinia was connected during the Oligocene. Of particular interest are the three stygobiotic species of Trichoniscidae occurring in the karst areas of central-eastern Sardinia. One of these species, Utopioniscus kuheni, was considered to be a very primitive taxon. The other two species recently discovered in caves of the same karstic areas are new to science and show intermediate morphological characters between the troglobiotic and endogean Alpioniscus species present on the island and U. kuehni. A molecular analysis shows that all the three aquatic species of Trichoniscidae are included in the same clade with Alpioniscus species, suggesting that U. kuehni is not the most primitive Trichoniscidae but rather a species of Alpioniscus secondarily adapted to an aquatic way of life.