Water mites (Acari, Hydrachnidia) are a significant component of freshwater ecosystems inhabiting a wide range of aquatic habitats. This study provides a first comprehensive DNA barcode library for the water mites of Montenegro. DNA barcodes were analysed from 233 specimens of water mites morphologically assigned to 86 species from 28 genera and 15 families. In the course of the study, four species, i.e. Lebertia reticulata (Koenike, 1919), Atractides inflatipalpis K.Viets, 1950, A. latipes (Szalay, 1935) and Parabrachypoda montii (Maglio, 1924) were molecularly confirmed as new for Montenegro and three species, i.e. Protzia octopora Lundblad, 1954, Piona laminata (Thor, 1901) and Unionicola ypsilophora (Bonz, 1783) are new for the Balkan Peninsula. Results are analysed using the Barcode Index Number system (BIN) and the Refined Single Linkage (RESL) of BOLD. The BIN assigned sequences to 98 clusters, while the RESL reveal 103 operational taxonomic units (OTUs). Unique BINs were revealed for 72 species (83.7%), whereas twelve species (14%) were characterised by two BINs and two species (2.3%) with three BINs. Amongst the studied taxa, 14 species were found with a high intraspecific sequence divergences (˃ 2.2%), emphasising the need for additional comprehensive morphological and molecu­lar analysis of these species.

Hygrobates specimens with a coarse lineated soft integument generally have been considered as representatives of H. calliger Piersig, 1896, regarded as a common and widely distributed species in the Palaearctic. In the present study using an integrative taxonomic approach that combines morphological studies and DNA barcoding we show that Hygrobates calliger-like mites belong to six distinct lineages. Two species, Hygrobates ponticus sp. nov. (East Türkiye, Georgia) and H. tyrrhenicus sp. nov. (Corsica) are described as new to science.

Using the example of a regulated stretch of the Krąpiel River (NW Poland), an analysis of the impact of dredging on the aquatic beetle (Coleoptera) fauna was made. After dredging the beetle fauna became markedly poorer quantitatively and had lower species diversity. Moreover, the qualitative composition and dominance structure were highly transformed. However, species number and diversity increased rapidly and were restored within just half a year. The structure of the restored fauna was most strongly influenced by vegetation, flow velocity and bottom sediment composition. The first to colonize the river were eurytopic beetles and species typical of small water bodies, which had significant refuges in the form of fish ponds bordering on the river; these species dominated the assemblage throughout the study period. Rheophiles with less dispersal power appeared later, and finally rheobionts, in low numbers but occupying an increasing number of sampling sites.

This study presents the first results from the analysis of water mites collected in Portugal as part of the Biodiversity Genomics Europe project. 307 COI DNA barcodes clustered into 75 BINs are provided, with 38 BINs being unique and deposited for the first time in the Barcode of Life Data Systems (BOLD). 65 species have been identified, of which 36 are new to the water mite fauna of Portugal. Two species, Torrenticola soniae Pešić, sp. nov. and T. elisabethae Pešić, sp. nov. (Torrenticolidae), are described as new to science. 47% of the water mite species currently known from Portugal now have reference barcodes in BOLD. High intraspecific distances were recorded for some species, suggesting the presence of cryptic diversity and species complexes that needs further study. Our results improve the DNA barcode reference database for Portuguese water mites, enhancing species identification accuracy and stimulating future investigation.

New records of water mites collected in 2022 and 2023 from northeastern Iran and southwestern Turkiye, are presented. DNA barcodes of 58 specimens, morphologically assigned to 13 species were newly generated. An integrative approach that combines morphology and DNA barcodes revealed three new species for water mite fauna of Türkiye, i.e. Lebertia variolata Gerecke, 2009, Torrenticola baueri Bader & Sepasgozarian, 1987 and Atractides zagrosensis Pešić, Saboori & Asadi, 2016, significantly widening their so far known area of distribution. Torrenticola ramini Bader, 1988, is reported for the first time since its original description, and T. eseni sp. nov. is described as new to science.