A Comprehensive Occurrence Dataset for European Ostracoda Inhabiting Groundwater and Groundwater‐Dependent Ecosystems

Motivation: Groundwater ecosystems sustain a unique and globally important biodiversity but remain understudied due to sampling and exploration challenges, as well as a shortage of taxonomic experts. Groundwater ostracods, like other groundwa- ter taxa, exhibit a high degree of endemism, rarity and subterranean specialisation, positioning them as potentially vulnerable organisms. To better understand biodiversity patterns and the conservation needs of this highly diverse group, we assembled a team of experts to gather the most comprehensive information available about groundwater ostracods in Europe. We present a dataset comprising 2065 occurrence records of 110 species, 11 undescribed species and 5 subspecies of groundwater ostracods. This open dataset may support future research on the distribution, evolutionary pathways and conservation needs of European groundwater ostracods, as well as inspire targeted sampling efforts in regions with currently limited data available. Main Types of Variables Contained: Occurrence records of groundwater ostracods, with details about taxonomy, source of records, occurrence locality, habitat type and species dependence on groundwater (obligate [stygobiont] versus facultative groundwater-­ dwellers [stygophile]). Spatial Location and Grain: Geographical Europe, spanning 32 countries. Occurrence records were assigned decimal degrees coordinates (EPSG:4326). Most occurrence records are at 100 m resolution. Time Period: 1915–2024. Major Taxa and Level of Measurement: Crustacea: Ostracoda. Most records have species or subspecies-­ level identification, while some are identified to genus or family levels. Software Format: Comma-­ separated values file (.csv) and Excel file (.xlsx), with UTF-­ 8 encoding and metadata provided fol- lowing the Darwin Core standard.