New records of ostracods (Crustacea, Ostracoda) from groundwater habitats in Italy, with faunistic and biogeographical notes

Groundwater ecosystems host highly specialised and frequently endemic faunas, yet their biodiversity remains poorly explored. Although Italy is recognised as a hotspot of subterranean diversity, knowledge of its stygobitic ostracods (i.e., species that are obligate inhabitants of subterranean waters) remains fragmentary. Here we report new data on ostracods collected from 15 natural caves, a mine and an aquifer across mainland Italy and Sicily between 2009 and 2018, with the aim of documenting new occurrence records from poorly investigated subterranean sites, discussing their taxonomic implications, and reassessing the diversity and endemism of Italian stygobitic ostracods in a broader European context. Nineteen taxa belonging to 12 genera and five families were identified, several of which are regarded as strictly stygobitic. These include representatives of Mixtacandona (Candonidae), among which several putative undescribed species of the laisi-chappuisi group were detected. Particularly noteworthy is the occurrence of Mixtacandona cf. botosaneanui in southern Italy: if its identity with the nominal species is confirmed, this record would considerably extend its known geographical range and provide the first description of the male, thereby adding important taxonomic information for a poorly known subterranean lineage. We also report a new record of Typhlocypris cf. eremita and specimens referable to Pseudolimnocythere, further expanding the known distribution of these genera within Italian subterranean habitats. Although some specimens could be assigned only tentatively because well-preserved adults were scarce, the new records substantially refine current knowledge of Italian groundwater ostracod diversity and distribution patterns at both regional and European scales. An updated checklist raises the number of Italian stygobitic ostracods to more than 30 taxa, representing approximately 30% of the currently known European groundwater ostracod diversity. This proportion is remarkable given the limited extent of Italian territory, and the high frequency of endemic and potentially undescribed species further highlights the Italian peninsula and its islands as important centres of diversification for subterranean ostracods. These results emphasize the need for continued biospeleological surveys and integrative taxonomic approaches combining morphology and molecular data to resolve species boundaries, phylogenetic relationships and colonization histories in subterranean lineages.