Barcoding reveals a remarkable genetic diversity of pontarachnid mites (Pontarachnidae, Hydrachnidia) in the Adriatic Sea, including the description of a new species from Slovenia

The family Pontarachnidae is found worldwide, mainly in coastal marine habitats; however, the diversity (and especially the ecology) of this poorly studied and mostly neglected group of marine meiofauna still awaits discovery. In this study, we present data on Mediterranean pontarachnids based on extensive material from the Adriatic and Tyrrhenian seas. Up to now, only one sequence of a pontarachnid mite from the Mediterranean was present in GenBank; we are adding 81 new pontarachnid mite barcodes from these Mediterranean areas to the DNA barcode library. Our study, using the DNA barcode fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene, shows that the coast of Slovenia harbours at least six genetic lineages representing distinct Molecular Operational Taxonomic Units (MOTUs), corresponding with six species of pontarachnid mites (three Litarachna Walter, 1925 and three Pontarachna; Philippi, 1840). The material from the Adriatic Sea (Piran, Slovenia) also revealed a new species, Litarachna cursusmaritima sp. nov., clearly separated from the hitherto known species by COI and by a very conspicuous dorsal colour pattern. Finally, the finding of two species, L. communis and P. punctulum, each represented by two Barcode Index Numbers (BINs) with relatively high genetic distance between morphologically similar populations from the Adriatic and the Tyrrhenian Sea, clearly shows the necessity of finding and using new morphological characters, such as colour pattern and applying new markers such as nuclear genes, to reveal possible cryptic or pseudocryptic diversity in pontarachnid mites.