Epikarst Drives Speciation in Stygobiotic Harpacticoid Copepods: An Integrative Taxonomic Study of <i>Elaphoidella</i> in the Western Carpathians with Description of a New Species

ABSTRACT This study examines cryptic diversity and speciation processes within stygobiotic harpacticoid copepods of the genus Elaphoidella , which inhabit the epikarst of the Demänová Valley Karst in Slovakia. Using an integrative taxonomic approach, we employed molecular phylogenetic analyses of COI and 28S rRNA gene fragments, molecular species delimitation methods, and traditional taxonomy to describe a new species, Elaphoidella droppai sp. n. Genetic data revealed significant divergence between E. droppai sp. n. and E. phreatica , which was supported by distinct clustering in phylogenetic trees. Molecular species delimitation methods consistently identified E. droppai sp. n. as a separate evolutionary unit. Despite sharing the same swimming leg pattern, notable morphological differences were observed, particularly in the P5, the furca, and the row of spines on the anal segment. The highly reduced female P5 represents a unique feature within Elaphoidella . Further analysis of the genital segments of females in both species revealed significant differences in segment dimensions and genital pore structure, suggesting reproductive isolation. These findings demonstrate that karstic vadose zones, particularly the epikarst, can act as a driver of speciation in subterranean fauna and a reservoir of hidden biodiversity. This integrative taxonomic study not only expands the known diversity of Elaphoidella in the Carpathian region but also underscores the importance of integrating genetic and morphological data for species discovery and understanding evolutionary processes in isolated subterranean habitats.