A new extremophile species of Pseudocandona (Crustacea, Ostracoda) from a sulfidic cave in Albania

Subterranean ecosystems host highly specialized and often endemic crustacean faunas, yet ostracods inhabiting chemically extreme sulfidic caves remain poorly documented. In this study, a new stygobiont species of the genus Pseudocandona is described from a sulfidic cave in Albania using an integrative taxonomic approach combining detailed morphological analyses and molecular data. Subterranean ostracods exhibit a suite of morphological, physiological, and life-history adaptations to the energetic constraints of groundwater habitats, and species thriving in sulfidic systems additionally tolerate high concentrations of hydrogen sulfide and hypoxia. The new species, Pseudocandona sulphurella sp. nov., belongs to the rostrata group, a clade otherwise dominated by surface-water taxa and with only one previously known stygobiont representative. Its valves and soft parts are frequently covered by sulfur-oxidizing bacterial epibionts, a feature shared with other crustaceans from sulfidic environments and potentially indicative of mutualistic interactions. Phylogenetic analyses based on COI and 28S sequences place the new species within a moderately supported clade of Western Palearctic Pseudocandona, while also highlighting the likely polyphyly of the genus. The discovery of P. sulphurella sp. nov. represents the first record of a stygobiont ostracod in Albania and expands current knowledge of biodiversity in chemoautotrophic subterranean ecosystems. This finding underscores the evolutionary significance of sulfidic caves as natural laboratories for studying adaptation, speciation, and the ecological dynamics of groundwater crustaceans.