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Shell shape of Unio species according to Zhadin's (1938) system: A, U. pictorum (ZSU-U3), B, U. tumidus (ZSUU9), C, U. crassus (ZISP-UC199). Superscripts indicate differing names after Starobogatov et al. (2004) 1 and Bogatov & Kijashko (2016) 2 : a, b U. limosus 1, 2 from Russia (INREC-UP1 and 2, and c from Ukraine (ZSU-U2); d, e, U. pictorum 1, 2 from Ukraine (ZSU-U1) and Russia (INREC-UP3b); f, g, U. rostratus 1 (= pictorum) 2 from Russia (INREC-UP3) and from Ukraine (ZSU-U4); h, U. protractus 1, 2 from Russia (INREC-UP3a). Genus 1 (subgenus) 2 Tumidiana: i, j U. (T.) conus 2 from Russia (INREC-UT8 and 9); k, l, U. (T.) tumidus 2 from Ukraine (ZSU-U7) and l, m, U. (T.) tumidus 2 from Russia (ZISP-UT221 and 114); n, T. muelleri 1 (= protractus 2 ) from Russia (INREC-UT6). Genus Crassiana 1, 2 : o, p, C. crassa 1, 2 from Russia (ZISPUC40) and from Ukraine (ZSU-U13); q, C. musiva 1 from Ukraine (ZSU-U11), r, C. fuscula 1 (syn. of C. musiva 2 ) (ZISP-UC1), s, C. nana 1, 2 (ZISP-UC2) and t, C. irgizlaica 1 (syn. of musiva 2 ) from Russia (INREC-UC8c). See Table 2 for collection numbers. Scale bar 1 cm.
Source publication
The taxonomy of species within the genus Unio (Bivalvia: Unionidae: Unioninae) in Russia and Ukraine has been contentious due to the lack of correspondence between three concurrent yet divergent classifications. In order to clarify which classification system best reflects the evolutionary relationships among these taxa, we performed detailed morph...
Contexts in source publication
Context 1
... The general shell shape of all analyzed putative comparatory species may be divided in three main forms in accordance with Zhadin's (1938) system, i.e., elliptical for U. pictorum, wedge-shaped for U. tumidus and oval for U. crassus ( Fig. ...
Context 2
... morphometric and molecular analyses performed in this study support the existence of three Unio species, U. pictorum, U. tumidus, and U. crassus, in Russia and Ukraine. Validity of these three species is corroborated by a different shell shape, umbo sculpture, tooth morphology (Figs. 2, 3, and 4), and also by soft anatomical features such as the differences on papillae morphology of the incurrent aperture and pigmentation of the excurrent aperture (Fig. 5E-G: f-g). Other anatomical features may also be useful for the definition of these three Unio species. For example, U. pictorum specimens always present a dark strip ...
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Citations
... Unioninae (Klishko et al. 2017). We found that the hinge structure of S. chinensis is similar to that of N. nuxpersicae but differs from that of Scabies crispata (Fig. 1, Table 7). ...
... Although a significant difference in shell shape between S. longata and regular N. douglasiae can be appreciated, these share a similar tooth structure (both have lamelliferous pseudocardinal teeth) (Fig. 1c, e). Nodularia douglasiae exhibits a wide distribution throughout East Asia, with highly variable shell shape ranging from elongate-oval to ovaterectangular and even ovate-wedge-shaped (Klishko et al. 2017;Lopes-Lima et al. 2017bGraf and Cummings 2021 Given the notable prevalence of endemism among freshwater mussels, the taxonomic classification of these organisms is intricately linked to the geographic distribution of species Konopleva et al. 2023). Freshwater mussel assemblages in the South-east Asian and East Asian subregions exhibit notable differences (Graf and Cummings 2007;Bolotov et al. 2018;Zieritz et al. 2018;Pfeiffer et al. 2021). ...
Effective species conservation necessitates the ability to accurately differentiate among species, a challenge compounded by taxonomic uncertainties in freshwater mussels due to substantial intraspecific variation and pronounced phenotypic plasticity in shell morphology. The taxonomic status and species validity of Scabies longata and S. chinensis, two species endemic in China, have been under continuous debate since establishment. The lack of essential molecular data required for a comprehensive systematic study has resulted in the unresolved taxonomic status of these two species. This study presents molecular data, including COI barcoding, COI + 28S rRNA, and mitogenomic data combined with morphological characteristics to assess the validity of S. longata and S. chinensis. Both morphological and COI barcoding data support the conclusion that S. longata and S. chinensis are junior synonyms of Nodularia douglasiae and N. nuxpersicae respectively. Our findings suggest the absence of Scabies species in China. Mitochondrial phylogenetic analyses were used to further elucidate intrageneric relationships within the genus Nodularia, revealing the following relationships: (N. breviconcha (Nodularia sp. 1 (N. douglasiae (N. nuxpersicae, N. nipponensis)))). We underscore the significance of employing an integrated taxonomic approach for species identification, especially given the considerable morphological disparities between larvae and adult freshwater mussels. Proper morphological identification of adult specimens is essential for extracting meaningful taxonomic characters. Furthermore, our findings suggest a notable resemblance between the freshwater bivalve fauna in southern China and those east of the Mekong River.
... Unio populations occupy a variety of different freshwater habitats, ranging from streams and rivers to lakes and wetlands (Lopes-Lima et al., 2017b). Species boundaries within the genus Unio are notoriously difficult to establish due to the high degree of intraspecific plasticity in shell morphology and the scarcity of diagnosable shell morphological characters across species (Zieritz et al., 2010;Prié and Puillandre, 2014;Klishko et al., 2017). For these reasons, Unio has many nominal taxa (more than 1,100), and its taxonomy and systematics were unstable until the mid-20th century (Graf, 2010). ...
... Within this range, U. pictorum can be distinguished from U. tumidus and U. crassus based on its more elongate, elliptical shape. The oldest fossils that are attributed to U. pictorum are from southwestern Siberia and the Middle Pliocene in age (Zykin, 1979(Zykin, , 2012Klishko et al., 2017; see Sup. Appendix 1). ...
The global decline of freshwater mussels and their crucial ecological services highlight the need to understand their phylogeny, phylogeography and patterns of genetic diversity to guide conservation efforts. Such knowledge is urgently needed for Unio crassus, a highly imperilled species originally widespread throughout Europe and southwest Asia. Recent studies have resurrected several species from synonymy based on mitochondrial data, revealing U. crassus to be a complex of cryptic species. To address long-standing taxonomic uncertainties hindering effective conservation, we integrate morphometric, phylogenetic, and phylogeographic analyses to examine species diversity within the U. crassus complex across its entire range. Phylogenetic analyses were performed using cytochrome c oxidase subunit I (815 specimens from 182 populations) and, for selected specimens, whole mi-togenome sequences and Anchored Hybrid Enrichment (AHE) data on ∼ 600 nuclear loci. Mito-nuclear discor-dance was detected, consistent with mitochondrial DNA gene flow between some species during the Pliocene and Pleistocene. Fossil-calibrated phylogenies based on AHE data support a Mediterranean origin for the U. crassus complex in the Early Miocene. The results of our integrative approach support 12 species in the group: the previously recognised Unio bruguierianus, Unio carneus, Unio crassus, Unio damascensis, Unio ionicus, Unio sesirmensis, and Unio tumidiformis, and the reinstatement of five nominal taxa: Unio desectus stat. rev., Unio gontierii stat. rev., Unio mardinensis stat. rev., Unio nanus stat. rev., and Unio vicarius stat. rev. Morphometric analyses of shell contours reveal important morphospace overlaps among these species, highlighting cryptic, but geographically structured, diversity. The distribution, taxonomy, phylogeography, and conservation of each species are succinctly described.
... The Unionidae family is rich in species diversity, with all members living in freshwater (Joyon, 2020). Freshwater mussels are an essential component of aquatic ecosystems and provide important ecosystem functions and services (Haukenes, 2013;Klishko et al., 2017). Mussels are sessile animals. ...
... Many freshwater mussel populations are declining worldwide. Unionid species are either threatened or endangered (Klishko et al., 2017). Deteriorating water quality is one of the most important reasons for the decline of freshwater mussels. ...
Common pollutants found in rivers include sewage, pesticides, heavy metals, nutrients from agricultural runoff, and pathogens. The resulting pollution can alter the physiological processes of living systems and cause environmental stress in aquatic environments. The need to monitor the effects of pollution in aquatic ecosystems has been driven by environmental and human health concerns. Freshwater mussels, which play an important role in freshwater ecosystems, are constantly exposed to a wide variety of contaminants as filter feeders. The sessile nature of mussels and their relatively long life span make them useful indicator species for monitoring and assessment of water quality. The aim of this study is to determine physiological stress in Unio stevenianus living in Karasu river, whose pollution level is increasing daily, by Cox gene expression. Real-time PCR analysis using β-actin as a reference gene was used for gene expression. The expression level of the Cox gene was higher in the Zeve region than in the Arısu region. The lower level in Arısu region indicates that water quality criteria are better in this region than in Zeve region. Expression studies should be carried out in U. stevenianus by selecting different genes specific to certain pollutants.
... With the advancement of molecular technology, significant progress in developing improved phylogenetic hypotheses for Unionidae has occurred in the past several decades (Graf, 2013;Huang et al., 2013;Klishko et al., 2017;Pavan-Kumar et al., 2022;Whelan et al., 2011;Wu et al., 2019). Specifically, phylogenetic analyses utilizing mitogenomes have the potential to effectively address both deep and shallow-level taxonomic puzzlers (Pfeiffer et al., 2019;Wu et al., 2020Wu et al., , 2022. ...
... Soft-body features such as the form and size of papillae in the incurrent aperture, pigmentation in the excur-rent aperture, etc., can be utilized for species delimitation and differentiation regardless of age or geographic origin (Bespalaya et al., 2023;Klishko et al., 2014Klishko et al., , 2017. Our findings reveal significant variations in the incurrent aperture, excurrent aperture, and gill between Lepidodesma aligera and Lepidodesma languilati. ...
Increasingly sophisticated molecular techniques and research tools have greatly advanced the understanding of species diversity and phylogenetic relationships in freshwater mussels. However, malacologists have been puzzled by the taxonomic position and species validity of certain species, particularly those described solely based on conchological characteristics. The genus Lepidodesma is one such group. Here, we integrate shell morphology, soft-body anatomy, and molecular phylog-eny to delimit the species validity of Lepidodesma aligera (Heude in Conchyliologie Fluviatile de la Provoince de Nanking 3:17-24, 1877) and Lepidodesma languilati (Heude in Journal De Conchyliologie 22:112-118, 1874). Comparative morphology reveals that L. aligera can be distinguished from L. languilati by its higher post-dorsal wing covered with scattered nodules, as well as differences in the incurrent aperture, excurrent aperture, and gill. Additionally, the average genetic distance based on DNA barcodes (COI) between both species is 4.0%. Integrative taxonomy supports the distinct species of L. aligera, rather than synonymy for L. languilati. Mitochondrial phylogenomic analyses confirm four monophyletic groups (Ambleminae + (Gonideinae + (Unioninae + Parreysiinae))) within the family Unionidae. L. aligera and L. languilati have a well-supported sister-group relationship and form a basal clade splitting from the rest of Unioninae. Therefore, the genus Lepidodesma should be classified as Lepidodesmini in Unioninae. The molecular clock with fossil calibration indicates that Lepidodesma originated in the Early Cretaceous (~121.30 Mya, 95% HPD = 90.37-156.54 Mya) and diverged in the Middle Neogene (~12.94 Mya, 95% HPD = 6.72-22.13 Mya). This study firstly provides anatomical features and molecular data for L. aligera and demonstrates the species validity and the systematic position of Lepidodesma taxa, which enrich our understanding of this rare group and facilitate its management and conservation.
... Altogether, morphospecies of the Unionidae needs complete revising on the basis of the integrative taxonomic method, examining topotypes and type series and also studying the interand intraspecific diversity in genetic and morphological features. In this regard, valuable steps have been taken in the right course by Bolotov et al. (2015), Klishko et al. (2017), and Sayenko et al. (2017). ...
Some members of the genus Sinanodonta (Modell, 1944) are known as successful invaders of freshwater habitats. Here we report the first record of Sinanodonta lauta (Martens, 1877) from Iran and provide morphological and molecular data on this alien population. This species was observed in the Dez River and a fish farm in Khuzestan, south of Iran. The S. lauta introduction seems to be closely related to the introduction of Asian carps from East Asia. The individuals collected from the river exhibited two COI haplotypes, probably due to several introduction events of host fish. Based on our haplotype network, the alien individuals found in Iran is closer to the native ones from South Korea (two-three substitutions) compared to other native individuals reported from Japan and Russian Far East. The presence of 10-11 years old specimens in Dez River shows that the species can survive well in the natural environment of southern Iran. Further expansion and colonization of S. lauta in south Iran or beyond it are not unexpected due to some human-mediated dispersal events as well as waterways in the region.
... Previously, these bivalves were found in the lower reaches of the Tobol River near Tobolsk Town [8], and, in 2021 and 2022, in the tributaries of the Irtysh River flowing from Ural Mountains (Tura, Pyshma, and Iset' rivers; unpublished data of E. Babushkin & M. Vinarski). Thus, there is reason to believe that the genus Unio has practically restored the previously lost part of its range, once located on the territory of the Irtysh River basin. 1 -the dates of the first finds or the dates of the first publications about them are indicated (then they coincide with earlier one in the last column); 2 -finds of U. pictorum in the upper Irtysh River basin need to be checked, we have no collections or photos of this species from this region, all our finds belong to the species U. tumidus; 3 -record of U. crassus from Lake Kenon [40] was based on erroneous identification and belong to U. tumidus see [37]. ...
Abstract: (1) This article reviews all available information on the species composition, current distribution, and origins of the neobiotic (non-indigenous and restoring the lost range) freshwater mollusks in Siberia. (2) An extensive literary search has been carried out, and virtually all existing publications of recent decades on the findings of freshwater mollusk species new to Siberia were taken into account. We examined extensive malacological collections of some of Russia's and Kazakhstan's scientific organizations. The core of the examined material is our own observations and collections made in various parts of Siberia and adjacent areas. (3) An annotated checklist of neobiotic species of mollusks reliably recorded in Siberia is presented, and probable mechanisms and "corridors" of infiltration of these species into the region are discussed. Most of the discovered snail species belong to a group popular among aquarists, and their source of introduction is obvious. Another large portion of species infiltrate into the region with the development of fish farming. A classification of species of neobiotic freshwater mollusks of Siberia was proposed and a forecast was made for changes in the Siberian freshwater malacofauna for the coming decades. (4) In our opinion, at present it is possible to accept the newest stage in the genesis of the freshwater malacofauna of Siberia, occurring in conditions specific to the Anthropocene.
Citation: Babushkin, E.S.; Nekhaev, I.O.; Vinarski, M.V.; Yanygina, L.V. Aliens and Returnees: Review of Neobiotic Species of Freshwater Mollusks in Siberia from the Kazakhstan Steppe to the Arctic Tundra. Diversity 2023, 15, 465.
... Freshwater mussel Unio tigridis Bourguignat, 1852 (Mollusca: Bivalvia: Unionidae) are a guild of stationary, suspended-feeding species that play vital roles in rivers and streams (Bolotov et al., 2019;Hamli and Al Asif, 2021;. Its essential aquatic ecosystem constituents, which perform significant ecological functions like nitrogen cycling, bioturbation that gives oxygen and habitat that other creatures need to survive, and increasing water clearance by filtration (Zieritz et al., 2016;Klishko et al., 2017;Lopes-Lima et al., 2021). ...
... In Iraq, the first recorded of this species in Habbaniya Lake by Najim (1959), in Euphrates by Al-Bassam (2005), and in the Greater Zab River by Ali (2007). Previously, Unionid mussels' species depended on shell traits for identification before the development of molecular technology (Lopes-Lima et al., 2017). However, it depending alone on shell morphology found difficult, due to the morphological convergences between species and the high level of phenotypic variability within species (Klishko et al., 2017). ...
... Previously, Unionid mussels' species depended on shell traits for identification before the development of molecular technology (Lopes-Lima et al., 2017). However, it depending alone on shell morphology found difficult, due to the morphological convergences between species and the high level of phenotypic variability within species (Klishko et al., 2017). Several newly released studies that used region of cytochrome oxidase subunit I gene of mitochondrial DNA (mt DNA-COI) for the biogeography and relationships of aquatic mussels in various Asiatic regions fundamentally altered our knowledge of diversity patterns (Choi, 2016;Lopes-Lima et al., 2020). ...
Freshwater mussels are a guild of stationary, suspended-feeding species; they perform significant ecological functions like nitrogen cycling, bioturbation that gives oxygen and habitat that other creatures need to survive, and increasing water clearance by filtration. Knowledge of the freshwater mussel Unio tigridis Bourguignat, 1852, distribution, and molecular study in Iraq was inadequate. In the current study, this species of freshwater Mussels belonging to the family Unionidae was collected from different locations in the Greater Zab River, from April to August 2022. The average water temperature of the site was arranged between (17.8 to 36.1 C°). All previous studies in the Kurdistan Region and Iraq were based on morphological characters and the current study was the first report of Unio tigridis that was confirmed by molecular genetics and COI gene, analyzed phylogenetically using Maximum Likelihood and Maximum Parsimony Methods.
... The Unionoidea is an ecologically diverse and geographically widespread group of freshwater bivalve mollusks, including six families (Unionidae, Margaritiferidae, Hyriidae, Etheriidae, Mycetopodidae, and Iridinidae) (Graf, 2013). The morphology of unionid shells is the subject of active taxonomic studies (Klishko et al., 2017;Lopes-Lima et al., 2020;Sayenko et al., 2021). The glochidial shell consists of two layers. ...
... Nodularia douglasiae (Griffith and Pidgeon, 1833) is a widespread freshwater mussel from the family Unionidae, and its distribution extends from Vietnam in the south to the Russian Far East in the north. It also includes south of the Korean Peninsula, Kyushu, and Honshu islands in Japan (Graf and Cummings, 2007;Klishko et al., 2017Klishko et al., , 2018Lopes-Lima et al., 2020). Such a wide distribution and relatively high abundance of N. douglasiae make it an evaluable species for studies of the phylogeny and evolution of mussel taxa (Klishko et al., 2017(Klishko et al., , 2018Sano et al., 2017;Choi et al., 2020;Lopes-Lima et al., 2020;Sayenko et al., 2021), comparative internal (organs/tissues) and external (shell, teeth, hinge) gross anatomy (Sano et al., 2017;Sayenko et al., 2021), histology (Sayenko and Rasshchepkina, 2018), the behavior of both larvae and adult mussels (Liu et al., 2006;Taeubert et al., 2012;Itoh et al., 2021), and morphology of glochidial shells (Inaba, 1941(Inaba, , 1964Park and Kwon, 1993;Wu et al., 1999;Sayenko, 2006Sayenko, , 2008Sayenko, , 2015 among other aspects. ...
... It also includes south of the Korean Peninsula, Kyushu, and Honshu islands in Japan (Graf and Cummings, 2007;Klishko et al., 2017Klishko et al., , 2018Lopes-Lima et al., 2020). Such a wide distribution and relatively high abundance of N. douglasiae make it an evaluable species for studies of the phylogeny and evolution of mussel taxa (Klishko et al., 2017(Klishko et al., , 2018Sano et al., 2017;Choi et al., 2020;Lopes-Lima et al., 2020;Sayenko et al., 2021), comparative internal (organs/tissues) and external (shell, teeth, hinge) gross anatomy (Sano et al., 2017;Sayenko et al., 2021), histology (Sayenko and Rasshchepkina, 2018), the behavior of both larvae and adult mussels (Liu et al., 2006;Taeubert et al., 2012;Itoh et al., 2021), and morphology of glochidial shells (Inaba, 1941(Inaba, , 1964Park and Kwon, 1993;Wu et al., 1999;Sayenko, 2006Sayenko, , 2008Sayenko, , 2015 among other aspects. First, brief descriptions of N. douglasiae glochidia were made using light microscopy for mussels from Korea (Inaba, 1941) and the Russian Far East (Antonova and Starobogatov, 1988). ...
Most freshwater mussels have an unusual life cycle that requires host fish species for larval (glochidia) development and dispersal. Glochidia have a unique morphological structure that adapts to parasitic lifestyles and survival. The morphology of the glochidial shells of most Unionoidea, a group of freshwater bivalve mollusks, has been studied in detail using light and scanning electron microscopy. This study summarizes our data on the glochidia shell morphology of the Asian mussel Nodularia douglasiae from two localities in the Primorsky Territory, the Russian Far East. In contrast to the shell morphology of glochidia, little is known about the neurodevelopment of the Unionoidea. Herein, we first demonstrate that the structures of the sensory, muscle, and nervous systems of the glochidia larvae of N. douglasiae differ dramatically from those of the comparable larval systems of marine bivalve species, as revealed through alpha-acetylated tubulin, serotonin (5-HT), and FMRFamide antibodies as well as phalloidin for detection of F-actin and whole-mount confocal microscopy. We found that the glochidia sensory system included four pairs of tubulin-lir multicilia hair cells. Non-ciliar tubulin-lir cells synthesize the neuropeptide FMRFamide and are identified as afferent neurons collecting information from peripheral tubulin-lir hair sensory cells to nervous regulators. The glochidia’s muscular system was represented by a smooth adductor, retractors, and minor muscle bundles associated with the shell and visceral organs. The 5-HT-lir larval system is arranged most simply and consists of two immunopositive neurons innervating the adductor. The FMRFamide-lir system is more complicated and consists of several neuronal centers comprising neuronal bodies and their neurites in different areas of the larva. The FMRFamide-lir neurons are closely associated with sensory hair cells, and others, together with 5-HT-lir neurons, may be involved in the anlagen of adult ganglia. Thus, the nervous system of N. douglasiae glochidia is drastically different from other mollusks and lophotrochozoans because of the absence of an apical organ and the location and composition of FMRFamide and 5-HT cells. Morphological, molecular, and behavioral investigations of Unionoidea taxa need to be further conducted to investigate the parasite-host relationship, nerve-dependent regulation of parasite behavior, and evolution of mollusks.
... Information about collected material is entered into international database [13]. Common methods of material collection (manually, at depths of 0.5 -2.5 m) and species identification were used [14]. During the study bioethics norms were observed, releasing researched species back into the reservoir after the study. ...
Species diversity and frequency index of bivalve mollusks’ of unionid family are researched within river basins of Ukraine. The largest frequency index of mussels is identified in the Prypiat and Desna basins (84 and 79% respectively), then (as the indicator declines) – the Dnieper and Severskiy Donets basins (74 and 67%), the Southern Bug and Danube (47 and 46%), the Southern and Western Bug (47 and 28%), the Crimea (17%). No mollusks were found in the Azov basin at all. Most often (33%) there were found groups consisting of only three unpretentious species ( Unio pictorum, U. tumidus, Anodonta anatina ). In general, settlements from one to three species make up 70% of all researched collecting sites. Settlements formed by four species are identified only in 23% of habitats. Only 6% of settlements consisted of five aboriginal species and about 1% – of six. Locations where six species lived together were identified only in the Danube and Prypiat basins. There are no settlements of five species in the Western Bug and Desna basins at all, and there are not any even four species settlements in the Crimea. The obtained data can be used for organizing environmental activities and assessing water environment quality
... Most recently, Klishko et al. (2017) discussed the records of Unio species in Transbaikalia (Eastern Siberia), in Lake Kenon, which serves as a cooling reservoir for the thermal power station in the city of Chita. In 2009-2013 the first records of Unio mussels from the Bukhtarma Reservoir, located in East Kazakhstan, in the upper courses of the Irtysh River, were published (Devyatkov, 2013(Devyatkov, , 2009Yanygina, 2016). ...
... For the species identification, we used the data of some publications on the taxonomy of unionid mussels Klishko et al., 2017;Zhadin, 1952) as well as some shell images available from the MUSSELp online database (Graf and Cummings, 2021b). The museum specimens represented by dried shells were identified based on conchological features (shell shape and proportions, shell surface sculpture and coloration, and the hinge structure). ...
... List of Unio localities in Russia and Kazakhstan east of the Ural Ridge. The numbers of localities in the table correspond to those in the map (Fig. 1 Klishko et al., 2017 between 1932 and 1934 (see Vinarski, 2020 for details). Notably, that, though the malacofauna of the Tom' River basin was studied intensively in the 1950-1970 s (Ioganzen, 1951;Ioganzen andNovikov, 1971, 1969;Novikov, 1971), no record of this genus was published in these decades. ...
Unionidae is a species-rich family of large freshwater mussels with an almost worldwide distribution. In many regions of the world, these mussels are imperiled. Northern Asia, excluding the Far East, is an excellent example of a region with a sharply impoverished fauna of the Unionidae as recently thought with one native species. Since the end of the 19th century, two freshwater mussel species of the genus Unio (U. pictorum and U. tumidus) were repeatedly recorded in Siberia. In the course of this study, these finds are confirmed both morphologically and genetically, the number of known occurrences of these mussels in the waterbodies of Asiatic Russia and Kazakhstan has drastically increased, and the third species, globally endangered U. crassus, was found in the Ob' River basin. The unique U. tumidus haplotype discovered from the Upper Irtysh River basin is of probable relic origin, which may indicate the presence of a Pleistocene refugium there. Due to natural environmental changes during the last century, several genera of freshwater Mollusca that previously inhabited Western Siberia, but went completely extinct in the Pleistocene, have started to recover the North Asiatic part of their former ranges. The case of Unio is exceptional since the recovery of its lost range goes not exclusively with the humans' help but also involves the natural mechanisms of dispersal and range extension, and also because these mussels are disappearing in other parts of the world and are placed in the IUCN Red List of Threatened Species.
