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DNA barcoding using a fragment of the mitochondrial cytochrome c oxidase subunit 1 gene (COI) has proven to be successful for species-level identification in many animal groups. However, most studies have been focused on relatively small datasets or on large datasets of taxonomically high-ranked groups. We explore the quality of DNA barcodes to delimit species in the diverse chironomid genus Tanytarsus (Diptera: Chironomidae) by using different analytical tools. The genus Tanytarsus is the most species-rich taxon of tribe Tanytarsini (Diptera: Chironomidae) with more than 400 species worldwide, some of which can be notoriously difficult to identify to species-level using morphology. Our dataset, based on sequences generated from own material and publicly available data in BOLD, consist of 2790 DNA barcodes with a fragment length of at least 500 base pairs. A neighbor joining tree of this dataset comprises 131 well separated clusters representing 121 morphological species of Tanytarsus: 77 named, 16 unnamed and 28 unidentified theoretical species. For our geographically widespread dataset, DNA barcodes unambiguously discriminate 94.6% of the Tanytarsus species recognized through prior morphological study. Deep intraspecific divergences exist in some species complexes, and need further taxonomic studies using appropriate nuclear markers as well as morphological and ecological data to be resolved. The DNA barcodes cluster into 120–242 molecular operational taxonomic units (OTUs) depending on whether Objective Clustering, Automatic Barcode Gap Discovery (ABGD), Generalized Mixed Yule Coalescent model (GMYC), Poisson Tree Process (PTP), subjective evaluation of the neighbor joining tree or Barcode Index Numbers (BINs) are used. We suggest that a 4–5% threshold is appropriate to delineate species of Tanytarsus non-biting midges.

Because the family Chironomidae, or non-biting midges, is one of the most species-rich groups of macroinvertebrates in freshwater habitats, species-level identifications of chironomids are important for biodiversity assessments in these ecosystems. Morphology-based species identifications from adult female chironomids usually are considerably more difficult than from adult males, or even impossible; thus, the females are often neglected in community assessments. We used DNA barcoding to investigate how inclusion of the females influenced the species count from springs and spring brooks at Sølendet Nature Reserve in Central Norway. By means of the barcodes we were able to identify 77.6% of the females to species by associating them with males from the study site or from other regions, whereas the remaining, unassociated females could be identified to genus level only. The number of recorded species increased by 27% when females were included. We also found that DNA barcoding is effective for the detection of taxonomically challenging species and species groups. Using DNA barcoding in combination with traditional taxonomy, we recognised at least five species new to science and three species and one genus new to Norway.

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Water mites of the genus Hygrobates are widely distributed in all biogeographic regions except the Antarctic. Palaearctic Hygrobates species with reticulated soft integument generally have been considered as representatives of one common and widely distributed species, Hygrobates fluviatilis Strøm, 1768. Based on partial COI sequences (DNA-barcodes) and statistical analysis of morphological data, we show that these mites belong to six distinct lineages. Two of them are widely distributed in Central Europe: Hygrobates fluviatilis here redescribed based on a neotype designated from the type locality in Norway, and a species new to science, H. arenarius Smit & Pešić. The four remaining lineages represent additional species new to science that appear to have more restricted distributions: H. corsicus Pešić & Smit (Corsica, Sardinia), H. marezaensis Pešić & Dabert (Montenegro, Albania, Croatia), H. turcicus Pešić, Esen & Dabert (Turkey), and H. persicus Pešić & Asadi (Iran, E Turkey). Statistical morphometric analysis reveals that the latter two species cannot be separated on morphological characters and should be considered true cryptic species. We provide data concerning biology and geographical distributions together with a key to all species of the complex.

For over a decade, DNA barcoding has proven an effective modern tool in taxonomy, evolutionary biology and biodiversity research. Many new species have been discovered and described with DNA barcodes as part of their diagnostic features. Using DNA barcodes, we uncovered a number of potential species within the Tanytarsus curticornis and Tanytarsus heusdensis species complexes (Diptera: Chironomidae) and detected morphological differences a posteriori that support the description of new species. Unusually large intraspecific divergence in COI p-distance (up to 10%) was observed for two species complexes. In total, eight species new to science are described and figured: T. adustus sp. n., T. heberti sp. n., T. madeiraensis sp. n., T. pseudoheusdensis sp. n., T. songi sp. n., T. thomasi sp. n., T. tongmuensis sp. n. and T. wangi sp. n.. Tanytarsus reei and T. tamaoctavus are redescribed, and T. tusimatneous is listed as a new junior synonym of T. tamaduodecimus. The diagnostic characters of the remaining species of the complexes are discussed. Keys to males and pupae are given.

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