DNA-barcodes reveal that European populations attributed to Hygrobates longipalpis (Hermann, 1804), thus far considered a common inhabitant of standing and slowly flowing running waters all over the Western Palaearctic, represent two distinct lineages, both widely distributed over the continent. They are differentiated also from an ecological point of view, with specimens from standing waters ("clade I") separated from specimens collected in slowly running waters ("clade II"). Morphological examination revealed that, based on the length ratio of proximo- and distomedial setae on terminal segments of fourth legs, two morphospecies correspond to these two clades. As molecular examination of a specimen from the type locality of H. prosiliens Koenike, 1915 (Bremen, Heiligenrode) shows that it belongs to "clade I", populations from standing waters are attributed to that species. In view of the sketchy original description, loss of holotype and insufficient locality data of H. longipalpis, we arbitrarily assign to it stream-dwelling populations of "clade II" and designate a neotype.
We analyse the taxonomic structure of the Hygrobates nigromaculatus-complex from the Balkan Peninsula. We describe two new species: Hygrobates lacrima Pešić sp. nov. (Montenegro) and H. limnocrenicus Pešić sp. nov. (Montenegro, North Macedonia). Although both species are morphologically similar, the average K2P-distance between DNA-barcode sequences from H. limnocrenicus sp. nov. and its closest relative H. setosus was 12.43% (SD = 1.47), and between H. lacrima sp. nov. and its closest relative H. nigromaculatus 15.87% (SD = 1.74). The new species exhibit distinct differences in terms of habitat preference: H. lacrima sp. nov. inhabits pools and shallow eddies along faster flowing waters, whereas H. limnocrenicus sp. nov. prefers deeper, fast flowing water, typically found in the outflow of a limnocrenic springs or lake outlets. The finding of these two new species suggests that efforts to investigate mites of the H. nigromaculatus-complex in the Balkans should be intensified.
Arrenurus (Arrenuridae) is the most species-rich genus of mites with about 950 named species that inhabit standing, and to a lesser extent, running water habitats around the world. To date, distinguishing species of Arrenurus has been based on male reproductive morphology. Here, we use morphological and molecular approaches to examine species boundaries among 42 named species of Arrenurus, including four named species that have colour variants (red and green A. americanus, and red and blue A. intermedius, A. manubriator and A. apetiolatus), and two unnamed morphospecies. In this study, we examine male genital structures with the use of SEM techniques, and apply mitochondrial (COI barcode region) and nuclear (28S rRNA) gene fragments to test whether male morphology reflects species boundaries in Arrenurus assessed by molecular analyses. Our results reveal that male reproductive morphology parallels species boundaries as judged by molecular data. We discuss the cases of genetically poorly diversified, yet morphologically clearly defined named species. Moreover, we show that based on the species we examined, colour morphs within otherwise morphologically similar specimens represent within-species variation and, in the absence of other diagnostic traits, colour itself can be misleading in distinguishing species. Our outcomes on molecular taxonomy of Arrenurus provide a background for testing hypotheses about speciation rate in water mites.
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