Freshwater mussels of the Order Unionida provide important ecosystem functions and services, yet many of their populations are in decline. We comprehensively review the status of the 16 currently recognized species in Europe, collating for the first time their life-history traits, distribution, conservation status, habitat preferences, and main threats in order to suggest future management actions. In northern, central, and eastern Europe, a relatively homogeneous species composition is found in most basins. In southern Europe, despite the lower species richness, spatially restricted species make these basins a high conservation priority. Information on freshwater mussels in Europe is unevenly distributed with considerable differences in data quality and quantity among countries and species. To make conservation more effective in the future, we suggest greater international cooperation using standardized protocols and methods to monitor and manage European freshwater mussel diversity. Such an approach will not only help conserve this vulnerable group but also, through the protection of these important organisms, will offer wider benefits to freshwater ecosystems.

Intra- and interspecific variability, being at the very core of alpha taxonomy, has been a long-standing topic of debate among tardigrade taxonomists. Early studies tended to assume that tardigrades exhibit wide intraspecific variation. However, with more careful morphological studies, especially those incorporating molecular tools that allow for an independent verification of species identifications based on phenotypic traits, we now recognise that ranges of tardigrade intraspecific variability are narrower, and that differences between species may be more subtle than previously assumed. The taxonomic history of the genus Milnesium, and more specifically that of the nominal species, M. tardigradum described by Doyère in 1840, is a good illustration of the evolution of views on intraspecific variability in tardigrades. The assumption of wide intraspecific variability in claw morphology led Marcus (1928) to synonymise two species with different claw configurations, M. alpigenum and M. quadrifidum, with M. tardigradum. Currently claw configuration is recognised as one of the key diagnostic traits in the genus Milnesium, and the two species suppressed by Marcus have recently been suggested to be valid. In this study, we clarify the taxonomic status of M. alpigenum, a species that for nearly a century was considered invalid. We redescribe M. alpigenum, using a population collected from the locus typicus, by the means of integrative taxonomy, i.e. including light microscopy, scanning electron microscopy, ontogenetic observations, and genetic barcoding. Moreover, the redescription of M. alpigenum allowed us to verify the uncertain taxonomic status of two popular laboratory models that were originally considered to be M. tardigradum; though one was recently reidentified as M. cf. alpigenum. Our analysis showed that both laboratory strains, despite being morphologically and morphometrically nearly identical to M. alpigenum, in fact represent a new species, M. inceptum sp. nov.  The two species, being disnguishable only by statistical morphometry and/or DNA sequences, are the first example of pseudocryptic species in tardigrades.

61 sequences of cytochrome oxidase subunit 1 (COI), 570 bp long, from Central Europe (8), Slovenia (2), and from the Balkans (51: 6 from, Romania, 15 from Greece, 15 from Bulgaria, 6 from Serbia, and 9 from Montenegro), 33 of them new, together with 61 sequences of the ribosomal 18S, 450 bp long, all of them new, were analysed to infer the pattern of radiation of Bythinella in the Balkans. Thirty two nominal taxa of Bythinella (22 nominal species: B. austriaca, B. calimanica, B. charpentieri, B. compressa, B. dacica, B. dispersa, B. grossui, B. hansboetersi, B. luteola, B. micherdzinskii, B. molcsanyi, B. nonveilleri, B. pannonica, B. pesterica, B. radomani, B. rhodopensis, B. robiciana, B. schmidti, B. slaveyae, B. srednogorica, B. taraensis and B. viseuiana; one nominal subspecies: B. austriaca ehrmanni; and nine Greek species not yet described) were included, represented mostly by paratypes or at least topotypes, collected at 31 Balkan localities. The phylogeny, inferred on the combined data set with the ML approach, showed two large clades, although they were weakly supported. One of them comprised the Romanian and Montenegro populations, and one Serbian population, the other (less genetically diversified) consisted of one Serbian and all the Bulgarian/Greek populations. The origin of those two clades was dated, with the external data, to be more than 4.341±0753 MYA old, thus its origin was assigned to isolation by the Dacic Basin (part of Paratethys). All the Bulgarian populations presumably belong to one species, which may be assigned to the recent recolonisation of this territory from the south.

Diplura is a group of entognathous hexapods, often considered a sister group to insects. They play an important role in recycling organic matter in soil and subterranean terrestrial ecosystems. The Campodeidae is the most diverse family, divided into four subfamilies. The subfamily Plusiocampinae has a subterranean life-style with many species distributed in the Euro-Mediterranean area. The incertae sedis tachycampoids (“lignée Tachycampoïde”) is a group within the family Campodeidae that share with the Plusiocampinae a strong preference for subterranean habitats and several morphological characters, such as slender body shape, elongated appendages, considerable increment in the number of antennomeres and cercal articles, and complexity of sensorial structures. The present monograph provides a taxonomic revision of the subfamily Plusiocampinae and the genera belonging to the tachycampoid lineage from Europe and the Mediterranean region. It comprises detailed morphological descriptions and illustrations together with data on the habitats and distributions of 87 species, 10 subspecies and 11 affinis forms. Seven new species are described among those, namely: Plusiocampa (Plusiocampa) apollo Sendra, Giachino & Vailati sp. nov., P. (P.) chiosensis Sendra & Gasparo sp. nov., P. (P.) dublanskii Sendra & Turbanov sp. nov., P. (P.) hoffmanni Sendra & Paragamian sp. nov., P. (P.) rhea Sendra sp. nov., P. (P.) ternovensis Sendra & Borko sp. nov. and P. (Venetocampa) ferrani Sendra & Delić sp. nov.

The list of freshwater gastropods of Bulgaria, with data on their distribution, ecology and conservation status, was based on a critical overview of all available sources and unpublished materials. The total number of freshwater snail species hitherto recorded from Bulgaria is 120. Three species are regarded as extinct, two species were found only as subfossil remains. The most diverse families are Hydrobiidae (67 species), Planorbidae (15), and Lymnaeidae (11). The remaining families are represented by 1 to 4 species. Zoogeographical, ecological and conservation data are discussed.