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The depressed river mussel Pseudanodonta complanata (Rossmässler, 1835) is an endangered freshwater bivalve with sparse distribution across Europe. Despite its high conservation priority, available data on the current population genetics and biogeography of P. complanata are very limited. In this paper, we studied the genetic diversity and differentiation of P. complanata based on newly sequenced COI and ND1 gene fragments, and on available sequences from the NCBI GenBank. We discovered a localized and highly divergent lineage in the Don River basin and a widespread but low diversified lineage distributed from the Volga River basin to the Oise River in France. A star-like haplotype network, results of mismatch analysis, and significant negative values of neutrality tests reveal that the pan-European lineage went through a bottleneck event. The discovery of the separate lineage in the Don River basin is and additional evidence of the existence of Pleistocene glacial refugia in the south of the Russian Plain. Moreover, this finding confirms the significance of the Azov Sea drainage as a freshwater biodiversity hotspot of great conservation importance.

The ecological group of mussel-associated freshwater leeches (Hirudinea) contains facultative and obligate inhabitants of the mantle cavity of freshwater mussels (Unionida) from Asia, Africa, North America, and South America. Here, we report on the record of a mussel-associated leech in Europe and present a list of its freshwater bivalve hosts. The widespread leech species Helobdella stagnalis (Glossiphoniidae) was recovered as a facultative inhabitant of the mantle cavity of the native Anodonta anatina, Unio pictorum, and U. tumidus, and the non-native Sinanodonta woodiana (Unionidae). Globally, the freshwater mussel-associated leech assemblage contains 17 species, including four Helobdella representatives: H. lineata and H. modesta in North America, H. adiastola in South America, and H. stagnalis in Europe.

Leonardo Fea, an Italian explorer and traveler, sampled a comprehensive collection of continental Mollusca during his travels throughout the former British Burma (currently Myanmar) in 1885-1887. Cesare Maria Tapparone-Canefri, an Italian malacologist, studied this sample and published a paper with a description of numerous terrestrial and freshwater molluscan taxa new to science. This collection was partly deposited in the Museo Civico di Storia Naturale di Genova (MSNG), Italy and the Indian Museum (ZSI: Zoological Survey of India) in Kolkata. Here, we provide a re-analysis of C.M. Tapparone-Canefri’s Burmese Unionidae collection. Our study reveals that the type series of only four nominal taxa described by Tapparone-Canefri as new to science in 1889 are still available in the MSNG, i.e. Unio rectangularis, U. pulcher, U. protensus var. obtusatus, and U. marginalis var. subflabellata. The first taxon is a valid species belonging to the genus Yaukthwa, while U. pulcher and U. protensus var. obtusatus are considered here as junior synonyms of the widespread Lamellidens generosus, and the last nominal taxon corresponds to L. savadiensis. The MSNG collection also contains shell lots of Indochinella pugio pugio, I. pugio paradoxa, Indonaia andersoniana, Radiatula chaudhurii, R. mouhoti haungthayawensis, Lamellidens savadiensis, L. generosus, Yaukthwa nesemanni, and Y. zayleymanensis, most of which were listed in Tapparone-Canefri’s work under incorrect names. We revise all the freshwater mussel taxa listed by Tapparone-Canefri based on the original descriptions, available DNA sequences, morphological data, and biogeographic evidence. A freshwater mussel from the Haungthayaw River that was identified by Tapparone-Canefri as Unio exolescens is described here as Trapezoideus mitanensis sp. nov., a fourth species in this small Contradentini genus with a restricted range. Finally, new taxonomic opinions are proposed here for Leoparreysia tavoyensis, Trapezidens dolichorhynchus, Lamellidens generosus, and Lamellidens savadiensis.

The family Glossiphoniidae is a diverse and widespread clade of freshwater leeches, playing a significant role in functioning of aquatic ecosystems. The taxonomy and biogeography of leeches from temperate, subtropical, and tropical regions attracted much attention of zoologists, while their taxonomic richness and distribution in the Arctic are poorly understood. Here, we present an overview of the Eurasian Arctic Glossiphoniidae based on the most comprehensive occurrence and DNA sequence datasets sampled to date. This fauna contains 14 species, belonging to five genera and three subfamilies. One genus and five species are new to science and described here. The world’s northernmost occurrences of glossiphoniids are situated on the Taymyr Peninsula at 72° N, although further records at higher latitudes are expected. Most Arctic leeches are characterized by broad ranges crossing several climatic zones (e.g., Glossiphonia balcanica and G. nebulosa), although the distribution of two new species may be confined to the high-latitude areas. The Taymyr Peninsula with the nearby Putorana Plateau represents the most species-rich area (totally 9 species), while the European Arctic, Iceland, Kolyma Highland, and Chukotka Peninsula house depleted faunas (2–4 species per subregion). Finally, we show that the high-latitude melanism is a common phenomenon in glossiphoniid leeches.

The Mekong and Chao Phraya rivers harbor a species-rich freshwater mussel assemblage containing a large radiation of the Pseudodontini species. Members of the genera Bineurus Simpson 1900 and Thaiconcha Bolotov et al., 2020 primarily inhabit small and medium-sized tributaries of these rivers. Here, we present an integrative taxonomic review of these genus-level clades. We show that Bineurus contains four species: B. mouhotii (Lea, 1863), B. exilis (Morelet, 1866) stat. rev., B. anodontinum (Rochebrune, 1882) stat. rev., and B. loeiensis sp. nov. In its turn, Thaiconcha comprises three species: T. callifera (Martens, 1860), T. munelliptica sp. nov., and T. thaiensis sp. nov. Two species, Pseudodon ovalis Morlet, 1889 and P. thomsoni Morlet, 1884, are considered here as questionable taxa. These findings further highlight that Southeast Asia represents a significant evolutionary hotspot of freshwater mussels, which requires further international collaborative research and conservation efforts.

In this correspondence, we present a summary of taxonomic names of freshwater Mollusca introduced by Dr. Nguyen N. Thach, an enthusiastic and productive malacologist from Vietnam. We show that this researcher described one new genus and 12 new nominal species of freshwater molluscs from Southeast Asia. Two of these nominal species, Sinanodonta hunganhi Thach, 2016 and Lanceolaria bogani Thach, 2016 (Bivalvia: Unionidae), were already considered junior synonyms of S. jourdyi (Morlet, 1886) and L. fruhstorferi (Dautzenberg, 1900), respectively (Do et al. 2018; Đặng and Hố 2019). Here, we propose one more synonym for the invasive Golden Apple Snail as follows: Pomacea canaliculata (Lamarck, 1822) [=Pomacea thachi Huber in Thach, 2020 syn. nov.] (Gastropoda: Ampullariidae). Furthermore, we establish the formal synonymy for the following taxa: Taia Annandale, 1918 [=Boganmargarya Thach, 2018 syn. nov.]; Taia shanensis (Kobelt, 1909) [=Boganmargarya huberi Thach, 2018 syn. nov.] (Gastropoda: Viviparidae); Brotia henriettae (Gray in Griffith & Pidgeon, 1833) [=Brotia frankhuberi Thach, 2020 syn. nov.; Brotia bogani Thach & Huber in Thach, 2020 syn. nov.] (Gastropoda: Pachychilidae); Pila pesmei (Morlet, 1889) [=Pila huberi Thach, 2020 syn. nov.] (Gastropoda: Ampullariidae); and Paludomus andersoniana Nevill, 1877 [=Paludomus huberi Thach, 2020 syn. nov.] (Gastropoda: Paludomidae). Additionally, four nominal species are treated here as taxa inquirenda: Melanoides thachi Huber in Thach, 2020 (Gastropoda: Thiaridae), Trochoita frankohleri Thach & Huber in Thach, 2020 (Gastropoda: Viviparidae), Paracrostoma huberi Thach, 2018 (Gastropoda: Pachychilidae), and Pseudodon artbogani Thach & Huber in Thach, 2020 (Bivalvia: Unionidae). We also show that the publication date written on the title page of the book “New Shells of South Asia. Volume 2” (Thach, 2020a) is a bit misleading and that this book appeared in the printed form on 23 June 2020. The latter date is fixed here as the date of availability of taxonomic names introduced in this work. Finally, we present an annotated checklist of freshwater Mollusca described by N. N. Thach with approximate coordinates of the type localities and reference to corresponding river drainage basins.

The razor clam genus Novaculina Benson, 1830 (Bivalvia: Pharidae: Pharellinae) is a group of secondary freshwater bivalves. Four allopatric species in this genus are distributed throughout Asian freshwater drainages from the Ganges River in India to the Yangtze River in China. Here, we present several new occurrences of Novaculina myanmarensis and N. gangetica from Myanmar that were confirmed by means of a molecular approach. These occurrences expand our knowledge on the ranges of both species. Furthermore, we compiled an updated distribution map for all the species in this genus. Our phylogeographic research suggests that Novaculina myanmarensis colonized the Ayeyarwady Basin from rivers of the Salween Estuary (Donthami and Ataran rivers) during the Late Pleistocene. Conversely, Novaculina gangetica populations from Myanmar does not demonstrate any clear phylogeographic structure. At first glance, this pattern can also be caused by a (sub)recent (Pleistocene) immigration into coastal rivers of western Myanmar from the Ganges Basin, although this preliminary hypothesis is yet to be confirmed using DNA sequences of samples from India and Bangladesh. Finally, the taxonomic status of two doubtful nominal taxa initially described as Novaculina members is discussed, i.e. N. gangetica theobaldi Hanley & Theobald, 1874 and N. andamanensis Preston, 1908. These taxa are considered junior subjective synonyms of the estuarine bivalve species Cultellus maximus (Gmelin, 1791) (Pharidae) and Azorinus coarctatus (Gmelin, 1791) (Solecurtidae), respectively.

I this paper Sinosolenaia gen. nov. a new genus of ultra-elongate freshwater mussels (Bivalvia: Unionidae) is described from Vietnam and eastern China.

The bivalve genus Galatea Bruguière, 1797 (Venerida: Donacidae) was thought to contain exclusively brackish-water clams, the ranges of which are confined to estuaries and lower tidal parts of large rivers in West Africa. This genus was therefore included to the global freshwater bivalve checklists (Bogan 2013; Graf 2013) as a largely estuarine group. Conversely, a review of published data alongside our field surveys indicate that at least three populations of Galatea spp. largely occur in freshwater environment, i.e. those from the Sanaga (Cameroon), Niger (Nigeria), and Volta (Ghana) rivers. The systematic placement of these populations is unclear, as are the taxonomic status and validity of numerous nominal taxa described in this genus from a variety of localities throughout the Atlantic Coast of Africa (Angola to Senegal). We tentatively assign the populations from Niger and Volta to Galatea paradoxa (Born, 1778), while the Sanaga’s population is considered here as Galatea schwabi (Clench, 1929). However, these taxa do not share clear morphological differences and may belong to a single widespread species. In this study, we present the first DNA sequence data for a Galatea member, i.e. G. schwabi. Our COI phylogeny supports its placement within the family Donacidae suggesting sister relationships between Galatea and Donax Linnaeus, 1758. Most Galatea populations play a vital role for local riparian communities in West Africa as an intensively exploited food source. Furthermore, the clams are heavily threaten by anthropogenic impacts such as dam construction, riverbed substrate mining, and river pollution. The fishing loads and habitat degradation altogether lead to the rapid decreasing of Galatea populations in several water bodies, e.g. the Volta River in Ghana. It is impossible to develop conservation and management plans for these clams due to the lack of reliable species-level taxonomic concept of the genus. It is clear that the Galatea taxonomy and ecology need a thorough revision in the future based on DNA sequences of newly collected samples from all West African rivers, in which these remarkable clams occur.

Trapezidens Bolotov, Vikhrev & Konopleva, 2017 (Bivalvia: Unionidae: Lamellidentini) is a peculiar freshwater mussel genus, the range of which is confined to the Western Indochina Subregion (Myanmar). Here we show that this genus contains five allopatric species: Trapezidens angustior (Hanley & Theobald, 1876) from the Bago, Sittaung, and Bilin rivers; T. dolichorhynchus (Tapparone-Canefri, 1889) from the Ayeyarwady River; T. exolescens (Gould, 1843) from the Dawei River; T. scutum (Sowerby, 1868) from the Tanintharyi (Great Tenasserim) River; and T. yeti sp. nov. from the Ye River. Phylogenetically, Trapezidens angustior, T. dolichorhynchus, and T. yeti sp. nov. are closely related to each other, forming a species complex, while T. exolescens and T. scutum represent the most distant lineages within the genus. An updated synonymy for each species is compiled.

Here, we present an integrative review of the non-native Sinanodonta spp. from Kazakhstan based on molecular and morphological data. Sinanodonta woodiana (Lea, 1834) inhabits the Syr Darya River, while two species, S. woodiana and S. lauta (Martens, 1877), have established viable populations in the Ili River basin, a tributary of the Balkhash Lake. The latter species was probably introduced in 1961-1971 from the Sungari River, a Chinese tributary of the Amur River. A distribution map of the two Sinanodonta species spreading in Middle Asia is provided. In Kazakhstan and Uzbekistan, these species were recorded from endorheic drainages limiting their native expansion throughout the region, although further human-mediated dispersal events are expected. There are no reliable records of these alien freshwater mussels from Kyrgyzstan, Tajikistan, and Turkmenistan. Our study highlight that Sinanodonta lauta represents one more invasive lineage of the Asian pond mussels and that this East Asian species can successfully colonize plain water bodies of inland desert areas such as Middle Asia.

Freshwater mussels cannot spread through oceanic barriers and represent a suitable model to test the continental drift patterns. Here, we reconstruct the diversification of Oriental freshwater mussels (Unionidae) and revise their taxonomy. We show that the Indian Subcontinent harbors a rather taxonomically poor fauna, containing 25 freshwater mussel species from one subfamily (Parreysiinae). This subfamily most likely originated in East Gondwana in the Jurassic and its representatives arrived to Asia on two Gondwanan fragments (Indian Plate and Burma Terrane). We propose that the Burma Terrane was connected with the Indian Plate through the Greater India up to the terminal Cretaceous. Later on, during the entire Paleogene epoch, these blocks have served as isolated evolutionary hotspots for freshwater mussels. The Burma Terrane collided with mainland Asia in the Late Eocene, leading to the origin of the Mekong’s Indochinellini radiation. Our findings indicate that the Burma Terrane had played a major role as a Gondwanan “biotic ferry” alongside with the Indian Plate.

The fish leech Acipenserobdella volgensis (Hirudinea: Piscicolidae) is a rare and poorly known freshwater species, which is thought to be an obligate parasite of sturgeons. This leech has a disjunctive range in Europe and Eastern Siberia. Here, we estimate the phylogenetic affinities and host range of A. volgensis using a set of DNA sequences (COI and 18S rRNA gene fragments), field observation data, and a review of the body of literature. Based on a time-calibrated Bayesian phylogeny, we show that the European and Siberian lineages of A. volgensis have been separated since the latest Pliocene (mean age = 2.7 Ma). The analysis of available host records indicates that this leech is characterized by a broader host range as it was collected from fish belonging to four families (Acipenseridae, Cyprinidae, Salmonidae, and Esocidae). Conversely, only a few suitable primary hosts (six sturgeons, one cyprinid, and one salmonid fish) were confirmed by earlier research. Moreover, this leech could be considered a facultative mussel-associated species that uses bivalves (duck mussel Anodonta anatina; Unionidae) as shelter. Globally, three other piscicolid leeches have been recorded from the mantle cavity of bivalve molluscs, that is, the freshwater taxa Caspiobdella fadejewi and Alexandrobdella makhrovi, and the marine species Austrobdella coliumicus.

Here we describe a new subgenus and three new species of parasitic water mites in the genus Unionicola (Acari: Hydrachnidia) from Myanmar: Myanmarataxsubgen. nov., Unionicola (Myanmaratax) savadiensissubgen. and sp. nov. (hosts: Lamellidens savadiensis and L. generosus), U. (My.) generosasp. nov. (the same hosts), and U. (My.) trapezidenssp. nov. (hosts: Trapezidens dolichorhynchus and T. angustior). These taxa were identified based on a two-gene phylogenetic analysis (COI + 28S), which also confirms the division of the genus Unionicola into numerous subgenera. The new species are cryptic species, which are morphologically indistinguishable but strongly resemble U. (Prasadatax) brandti Vidrine, 1985 described from Thailand (hosts: Lens spp. and Ensidens spp.). We also transfer the latter taxon from Prasadatax to Myanmaratax based on a set of morphological evidence and propose U. (My.) brandticomb. nov. The new subgenus contains a total of five species, one of which needs future sampling efforts and will be described elsewhere. Additionally, 56 valid subgenera, which were placed in the synonymy of the genus and in one case raised to the genus level, are restored here until robust phylogenetic evidence on their taxonomic status is available. Our results also confirm that Unionicola mites are narrow host specialists that are associated with either one or a few closely related freshwater mussel species belonging to one or two sister genera.

Freshwater mussels are sensitive to habitat and water quality, revealing the fastest rates of human-mediated global extinction among aquatic animals. These animals are especially diverse in tropical Asia, the faunas of which are characterized by high levels of endemism. Here we describe four new species and four new subspecies of freshwater mussels from Myanmar. Leoparreysia whittenisp. nov., the smallest representative of this genus, was discovered from the Ayeyarwady and Chindwin rivers. Radiatula myitthanensissp. nov. and R. chindwinensissp. nov. were recorded from the Chindwin Basin, and R. mouhoti haungthayawensisssp. nov. has been discovered from the Haungthayaw River. Indochinella pugio has been revised with a description of three subspecies: I. pugio viridissimassp. nov. from the Sittaung, Bilin and Bago rivers, I. pugio daweiensisssp. nov. from the Dawei River, and I. pugio paradoxassp. nov. from the Haungthayaw River. Yaukthwa elongatulasp. nov., a peculiar species, conchologically resembling representatives of the genus Solenaia (Gonideinae) with ultra-elongated shell was found in the Chindwin Basin. Our records highlight that tropical Asia harbors numerous, but still overlooked local endemic lineages of freshwater bivalves, which may be on the brink of extinction due to the high anthropogenic and climate change impacts.

The systematics of Oriental freshwater mussels (Bivalvia: Unionidae) is poorly known. Here, we present an integrative revision of the genus Trapezoideus Simpson, 1900 to further understanding of freshwater mussel diversity in the region. We demonstrate that Trapezoideus as currently circumscribed is non-monophyletic, with its former species belonging to six other genera, one of which is new to science and described here. We recognize Trapezoideus as a monotypic genus, comprised of the type species, T. foliaceus. Trapezoideus comptus, T. misellus, T. pallegoixi, and T. peninsularis are transferred to the genus Contradens, T. subclathratus is moved to Indonaia, and T. theca is transferred to Lamellidens. Trapezoideus prashadi is found to be a junior synonym of Arcidopsis footei. Trapezoideus dallianus, T. nesemanni, T. panhai, T. peguensis, and two species new to science are placed in Yaukthwagen. nov. This genus appears to be endemic of the Western Indochina Subregion. The two new species, Yaukthwa paiensissp. nov. and Y. inlenensissp. nov., are both endemic to the Salween River basin. Our results highlight that Southeast Asia is a species-rich freshwater mussel diversity hotspot with numerous local endemic species, which are in need of special conservation efforts.

The data that supports the findings of this study are available in the supplementary material of this article., Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists., This publication is based upon work from COST Action CA18239, supported by COST (European Cooperation in Science and Technology). A.M.L. was financed by the Institute of Environmental Sciences Jagiellonian University (N18/DBS/000003) and K.N. by the Aragón Government. The authors acknowledge Jarosław Andrzejewski, Bartosz Czader, Anna Fica, Marcin Horbacz, Tomasz Jonderko, Steinar Kålås, Tomasz Kapela, Bjørn Mejdell Larsen, Maciej Pabijan, Katarzyna Pawlik, Ilona Popławska, Joanna Przybylska, Tomasz Przybył, Mateusz Rybak, Kjell Sandaas, Jarosław Słowikowski, Tomasz Szczasny, Michał Zawadzki and Paweł Zowada for providing detailed information on specific examples concerning freshwater mussels in anthropogenic habitats. We thank the editor and two anonymous referees for the valuable suggestions made, which increased the clarity of our manuscript.

Parasites and symbionts of freshwater mussels are poorly understood, although a diverse assemblage of mussel-associated leeches (Glossiphoniidae) was recently described. Here, we report on the discovery of a fish leech (Piscicolidae) in the mantle cavity of the freshwater mussel Cristaria plicata (Unionidae) in the Russian Far East. It is the first member of this leech family being associated with freshwater molluscs. This leech does not match any known genus and species both morphologically and genetically, and is described here as Alexandrobdella makhrovigen. & sp. nov. It uses mussels as shelter (and probably as a secondary host), while the Amur catfish Silurus asotus (Siluridae) seems to be the primary host. These novel findings indicate that mussel-associated leech assemblage contains at least one piscicolid species. Our fossil-calibrated phylogeny suggests that the crown group of Piscicolidae was originated in the Early Cretaceous. This primarily marine family shares at least five independent colonization events into freshwater environments.

While a growing body of modern phylogenetic research reveals that the Western Indochina represents a separate biogeographic subregion having a largely endemic freshwater fauna, the boundaries of this subregion are still unclear. We use freshwater mussels (Unionidae) as a model to reconstruct spatial patterns of freshwater biogeographic divides throughout Asia. Here, we present an updated freshwater biogeographic division of mainland Southeast Asia and describe 12 species and 4 genera of freshwater mussels new to science. We show that the Isthmus of Kra represents a significant southern biogeographic barrier between freshwater mussel faunas of the Western Indochina and Sundaland subregions, while the Indian and Western Indochina subregions are separated by the Naga Hills, Chin Hills, and Rakhine Yoma mountain ranges. Our findings highlight that the freshwater bivalve fauna of Southeast Asia primarily originated within three evolutionary hotspots (Western Indochina, Sundaland, and East Asian) supplemented by ancient immigrants from the Indian Subcontinent.

Amik Lake or, historically, Lake of Antioch, was a large freshwater body in the lower Orontes River basin (Hatay Province, Turkey) that was drained in the 1940s-1970s. Several endemic animal species were described from this lake, including the freshwater mussel Anodonta pseudodopsis Locard, 1883 (Bivalvia: Unionidae) characterized by a large rounded shell covered by a peculiar yellow or yellowish-brown periostracum. Molecular analyses of topotypes of this nominal taxon collected from the former lake’s tributaries in the Amik Plain indicate that it is an intra-specific lineage of the widespread Anodonta anatina (Linnaeus, 1758) based on the mitochondrial COI and 16S rRNA, and the nuclear 28S rRNA gene fragments. Geometric morphometric analyses using the lectotype and topotypes of Anodonta pseudodopsis support our DNA-based hypothesis on the status of this nominal taxon. A new synonymy is provided as follows: Anodonta anatina = Anodonta pseudodopsis syn. nov. The syntype of Anodonta pseudodopsis SMF 5129 “See von Antiochia” (Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany) is designated here to be the lectotype of this nominal taxon. Finally, we conclude that Anodonta anatina range covers the Orontes River basin in Turkey and Syria and the Nahr al-Kabir al-Shamali River in the Latakia Governorate of Syria. This intraspecific lineage of Anodonta anatina and other freshwater mussels of the Middle East are highly threatened due to multiple anthropogenic impacts and must be a focus of international conservation efforts. The Karasu River in eastern Turkey hosts viable populations of all freshwater mussel species of the Orontes’s fauna and can be considered one of the most important water bodies for the conservation of these imperiled animals in the region.

Southeast Asia harbors a unique and diverse freshwater fauna of Mesozoic origin, which is under severe threat of extinction because of rapid economic development and urbanization. The largest freshwater basins of the region are certainly the primary evolutionary hotspots and they attract the most attention as key biodiversity areas for conservation. In contrast, medium-sized rivers are considered low-importance areas with secondary biodiversity, whose faunas originated via founder events from larger basins during the Pleistocene, although such a scenario has never been tested by using a phylogenetic approach. In this investigation, we used freshwater mussels (Unionidae) as a model to estimate the levels of endemism within the Sittaung, a little-known remote basin in Myanmar, compared with the surrounding larger rivers (Irrawaddy, Salween and Mekong). We discovered that the Sittaung represents an exceptional evolutionary hotspot with numerous endemic taxa of freshwater mussels. On the basis of our extensive dataset, we describe two new tribes, two genera, seven species and a subspecies of Unionidae. Our results highlight that medium-sized basins may represent separate evolutionary hotspots that harbor a number of endemic lineages. These basins should therefore be a focus of special conservation efforts alongside the largest Southeast Asian rivers.

Freshwater mussels (Unionida) are one of the most imperiled animal groups worldwide, revealing the fastest rates of extinction. Habitat degradation, river pollution and climate change are the primary causes of global decline. However, biological threats for freshwater mussels are still poorly known. Here, we describe a diverse ecological group of leeches (Hirudinea: Glossiphoniidae) inhabiting the mantle cavity of freshwater mussels. So far, examples of mussel-associated leech species are recorded from East Asia, Southeast Asia, India and Nepal, Africa, and North America. This group comprises a dozen glossiphoniid species with a hidden life style inside the mantle cavity of their hosts largely overlooked by researchers. We show that the association with freshwater mussels evolved independently in three leech clades, i.e. Batracobdelloides, Hemiclepsis, and Placobdella, at least since the Miocene. Seven mussel-associated leech species and two additional free-living taxa are described here as new to science.

Uniorectangularis Tapparone-Canefri, 1889 is a little-known nominal species of freshwater mussels described from a tributary of the Ayeyarwady River in Myanmar. This taxon was considered a synonym of Gibbosulalaosensis (Lea, 1863), a margaritiferid species. However, the range of Gibbosulalaosensis does not encompass the Ayeyarwady River watershed. Here we re-examine the holotype of Uniorectangularis and provide a conchological re-description of this species. Based on conchological features such as the shell shape, elevated umbo, and the structure of lateral and pseudocardinal teeth, we transfer this taxon to the genus Indonaia Prashad, 1918 and propose I.rectangularis (Tapparone-Canefri, 1889), comb. nov. It appears to be a rare freshwater mussel species with a restricted range, because it has not been found since the original description. Two additional species in this genus are known from Myanmar, i.e. Indonaiaandersoniana (Nevill, 1877) and I.subclathrata (Martens, 1899).

Freshwater mussels are ecosystem engineers and keystone species in aquatic environments. Unfortunately, due to dramatic declines this fauna is among the most threatened globally. Here, we clarify the taxonomy and biogeography of Russian Unionidae species based on the most comprehensive multi-locus dataset sampled to date. We revise the distribution and assess the conservation status for each species. This fauna comprises 16 native species from 11 genera and 4 tribes: Anodonta, Pseudanodonta (Anodontini); Amuranodonta, Beringiana, Buldowskia, Cristaria, Sinanodonta (Cristariini); Middendorffinaia, Nodularia, Unio (Unionini); and Lanceolaria (Lanceolariini). No country-level endemic species are known in Russia, except for Buldowskia suifunica that may also occur in China. Sinanodonta woodiana, a non-native species, was introduced from China. Russia comprises the northern parts of Western and Eastern Palearctic subregions. The first subregion with six species encompasses a huge area from the western boundary of Russia to the Lena Basin in Siberia. The second subregion with 10 species covers the Amur Basin, rivers east of the Lena Basin, coastal basins of the Japan Sea, and the North Pacific Islands. The fauna of Russia primarily includes widespread generalist species that are here considered Least Concern (LC). However, Buldowskia suifunica and Sinanodonta lauta have restricted distributions and are assessed here as Vulnerable (VU) and Endangered (EN), respectively.

The Oriental Region harbours the second richest fauna of freshwater bivalves in the world, including many endangered endemic taxa. However, the Oriental fauna of the Unionidae have been very poorly studied using an integrative taxonomic approach, which may provide reasonable revisions of complicated (cryptic) taxa based on morphological, molecular, biogeographic and ecological evidence. Here, we present the first example of an integrative taxonomic revision concerning the status of Unio exolescens Gould (1843), a nominal mussel taxon that was accepted as a valid species within the genus Trapezoideus Simpson (1900). Currently, Trapezoideus exolescens is considered the type of the genus as far as the originally designated type species, U. foliaceus Gould (1843), was considered to be a synonym of T. exolescens. Using nucleotide sequences obtained from mitochondrial (COI and 16S rRNA) and nuclear (28S rDNA) genes, we found that the topotypes of Unio exolescens Gould (1843) cluster together with representative...

The taxonomy and biogeographic history of the bivalve family Margaritiferidae are controversial because previous molecular studies did not provide a well-resolved phylogenetic framework for these enigmatic freshwater mussels that have extensive but disjunct distribution in North America, Eurasia and North Africa. In this study, we present a new, fossil-calibrated phylogenetic hypothesis based on five molecular markers (∼4kb of total length) for ten species. Our results indicate that all recent margaritiferids are in the single genus, Margaritifera Schumacher, 1816. Additionally, we identified three relatively well-supported phylogenetic clades that are valid subgenera, i.e., Margaritifera s. str. (Holarctic), Margaritanopsis (=Cumberlandia) (southeast North America-southeast Asia disjunct) and Pseudunio (Mediterranean). We suggest that the crown lineage of the Margaritiferidae most likely originated in the Cretaceous (mean age 93Ma, 95% CI 66-126Ma). The combined results of ancestral area reconstructions based on the three different approaches (S-DIVA, DEC and S-DEC) showed that ancient vicariance events could have played an important role in speciation within the family. The rates of mitochondrial evolution of margaritiferids are notably slow, which may be associated with their longevity, long generation time and low metabolic rates. Our findings highlight the complex biogeographic history of the Margaritiferidae as an intermixing of ancient vicariance and dispersal events, which were most likely associated with some inland barriers, continental movements and a sea level dynamic.

Here we report the first molecular data on an invasive Sinanodonta woodiana ( Lea, 1834 ) (Bivalvia: Unionidae) population from Lesser Sundas (Flores Island, Indonesia). The DNA barcoding reveals that this population belongs to a mitochondrial lineage that is widely distributed across Malaysia. The mean COI p -distance between this ‘tropical’ lineage and invasive European populations is 5.3 ± 1.0% which clearly corresponds to the interspecific difference. The representatives of such a ‘tropical’ lineage have likely invaded other Indonesian islands together with the introduction of their host fish species, because our sequenced specimens were taken from a population on the southeastern edge of the current Sinanodonta distribution. The molecular identification of invasive populations of the Chinese pond mussels using available online databases such as the BOLD IDS and NCBI's Genbank is doubtful, because there are at least seven distinct mitochondrial lineages, hence each of them could belong to a separate cryptic taxon.

Freshwater mussels (Bivalvia: Unionidae) is a diverse family with around 700 species being widespread in the Northern Hemisphere and Africa. These animals fulfill key ecological functions and provide important services to humans. Unfortunately, populations have declined dramatically over the last century, rendering Unionidae one of the world’s most imperiled taxonomic groups. In Far East Asia (comprising Japan, Korea, and Eastern Russia), conservation actions have been hindered by a lack of basic information on the number, identity, distribution and phylogenetic relationships of species. Available knowledge is restricted to studies on national and sub-national levels. The present study aims to resolve the diversity, biogeography and evolutionary relationships of the Far East Asian Unionidae in a globally comprehensive phylogenetic and systematic context. We reassessed the systematics of all Unionidae species in the region, including newly collected specimens from across Japan, South Korea, and Russia, based on molecular (including molecular species delineation and a COI + 28S phylogeny) and comparative morphological analyses. Biogeographical patterns were then assessed based on available species distribution data from the authors and previous reference works. We revealed that Unionidae species richness in Far East Asia is 30% higher than previously assumed, counting 43 species (41 native + 2 alien) within two Unionidae subfamilies, the Unioninae (32 + 1) and Gonideinae (9 + 1). Four of these species are new to science, i.e. Beringiana gosannensis sp. nov., Beringiana fukuharai sp. nov., Buldowskia kamiyai sp. nov., and Koreosolenaia sitgyensis gen. & sp. nov. We also propose a replacement name for Nodularia sinulata, i.e. Nodularia breviconcha nom. nov. and describe a new tribe (Middendorffinaiini tribe nov.) within the Unioninae subfamily. Biogeographical patterns indicate that this fauna is related to that from China south to Vietnam until the Mekong River basin. The Japanese islands of Honshu, Shikoku, Kyushu, Hokkaido, and the Korean Peninsula were identified as areas of particularly high conservation value, owing to high rates of endemism, diversity and habitat loss. The genetically unique species within the genera Amuranodonta, Obovalis, Koreosolenaia gen. nov., and Middendorffinaia are of high conservation concern.

The razor clam genus Novaculina represents an example of a marine-derived, secondary freshwater group. It was thought to comprise three species: N. gangetica (Ganges and smaller basins in Bangladesh and northwestern Myanmar), N. siamensis (Bang Pakong and Pasak rivers in Thailand and Mekong River in Vietnam), and N. chinensis (lower Yangtze River, China). Here we describe Novaculina myanmarensis sp. nov., an additional species from the Ayeyarwady and Salween basins representing a divergent lineage that appears to be sister to N. gangetica. This new record closes a Novaculina range disjunction between northwestern Myanmar and Thailand. The populations of this novel species share a shallow molecular divergence from each other indicating potential dispersal events between the two distant freshwater basins during the Late Pleistocene. Our ancestral area modeling suggests that the MRCA of Novaculina crown group was a salt-tolerant freshwater species. The recent Novaculina species most likely originated via allopatric speciation. Our findings highlight that generalist estuarine species could have played the role as a source for bivalve expansions into freshwater and that western Indochina is a separate biogeographic subregion, which is clearly distinct from India. A new synonymy is proposed as follows: Pharellinae Stoliczka, 1870 = Novaculininae Ghosh, 1920 syn. nov.

The Sinanodonta woodiana species complex includes several cryptic species-level phylogenetic lineages, the taxonomic placement of which is unclear. Here, we present the results of molecular analyses of a Sinanodonta sample from Middle Asia (Uzbekistan). The COI haplotype of the Uzbekistan lineage is similar to those of invasive Sinanodonta populations from Europe, Russia and Myanmar. We show that the non-native Sinanodonta flocks in Europe and Middle Asia originated from a single source population in China. Our results reveal that the Sinanodonta woodiana species complex comprises at least six distinct biological species: S. cf. gibba (=temperate invasive lineage), S. cf. woodiana (=tropical invasive lineage), S. schrenkii (=S. amurensis), S. ovata, S. jourdyi, and S. lucida, and two phylogenetic lineages with uncertain taxonomic names.

The freshwater mussel genus Oxynaia Haas, 1911 is thought to be comprised of two geographically disjunct and morphologically variable species groups but the monophyly of this taxon has yet to be tested in any modern cladistic sense. This generic hypothesis has important systematic and biogeographic implications as Oxynaia is the type genus of the currently recognized tribe Oxynaiini (Parreysiinae) and is one of the few genera thought to cross several biogeographically important barriers in Southeast Asia. Morphological and molecular data clearly demonstrate that Oxynaia is not monophyletic, and the type species and its allies (O. jourdyi group) belong to the Unioninae, and more specifically as members of the genus Nodularia Conrad, 1853. Therefore, neither Oxynaiasyn. nov. nor Oxynaiini Starobogatov, 1970 are applicable to the Parreysiinae and in the absence of an available name, Indochinellagen. nov. and Indochinellini trib. nov. are described. Several combinations are proposed as follows: Indochinella pugio (Benson, 1862) gen. et comb. nov., Nodularia jourdyi (Morlet, 1886) comb. res., N. gladiator (Ancey, 1881) comb. res., N. diespiter (Mabille, 1887) comb. res. and N. micheloti (Morlet, 1886) comb. res. Finally, we provide an updated freshwater biogeographic division of Southeast Asia.

Macrobioerosion is a common process in marine ecosystems. Many types of rock-boring organisms break down hard substrates, particularly carbonate rocks and calcareous structures such as dead corals and shells. In paleontology, the presence of rocks with boreholes and fossil macroboring assemblage members is one of the primary diagnostic features of shallow marine paleo-environments. Here we describe a silicate rock-boring organism and an associated community in submerged siltstone rock outcrops in Kaladan River, Myanmar. The rock-boring mussel Lignopholas fluminalis is a close relative of the marine piddocks, and its borings belong to the ichnospecies Gastrochaenolites anauchen. The neotectonic uplift of the area leading to gradual decrease of the sea level with subsequent shift from estuarine to freshwater environment was the most likely driver for the origin of this community. Our findings highlight that rocks with macroborings are not an exclusive indicator of marine paleo-ecosystems, but may also reflect freshwater habitats., Macrobioerosion, the boring of rock and other hard substrates by living organisms, is used as a marker of marine paleo-environments. Here, Bolotov et al. describe a rock-boring mussel and its associated community from freshwater in Myanmar, demonstrating that macrobioerosion is a wider phenomenon.

The concept of long-lived (ancient) lakes has had a great influence on the development of evolutionary biogeography. According to this insight, a number of lakes on Earth have existed for several million years (e.g., Baikal and Tanganyika) and represent unique evolutionary hotspots with multiple intra-basin radiations. In contrast, rivers are usually considered to be variable systems, and the possibility of their long-term existence during geological epochs has never been tested. In this study, we reconstruct the history of freshwater basin interactions across continents based on the multi-locus fossil-calibrated phylogeny of freshwater mussels (Unionidae). These mussels most likely originated in Southeast and East Asia in the Jurassic, with the earliest expansions into North America and Africa (since the mid-Cretaceous) following the colonization of Europe and India (since the Paleocene). We discovered two ancient monophyletic mussel radiations (mean age ~51–55 Ma) within the paleo-Mekong catchment (i.e., the Mekong, Siam, and Malacca Straits paleo-river drainage basins). Our findings reveal that the Mekong may be considered a long-lived river that has existed throughout the entire Cenozoic epoch.

A well-established invasive Sinanodonta woodiana population was discovered in a floodplain lake of the upstream section of the Irrawaddy River basin, Kachin State, Myanmar. The DNA barcoding reveal...

The freshwater pearl mussel family Margaritiferidae includes 13 extant species, which are all listed by IUCN as endangered or vulnerable taxa. In this study, an extensive spatial sampling of Margaritifera spp. across the Russian Far East (Amur Basin, Kamchatka Peninsula, Kurile Archipelago and Sakhalin Island) was conducted for a revision of their taxonomy and distribution ranges. Based on their DNA sequences, shell and soft tissue morphology, three valid species were identified: Margaritifera dahurica (Middendorff, 1850), M. laevis (Haas, 1910) and M. middendorffi (Rosén, 1926). M. dahurica ranges across the Amur basin and some of the nearest river systems. M. laevis is distributed in Japan, Sakhalin Island and the Kurile Archipelago. M. middendorffi was previously considered an endemic species of the Kamchatka. However, it is widespread in the rivers of Kamchatka, Sakhalin Island, the Kurile Islands (across the Bussol Strait, which is the most significant biogeographical boundary within the archipelago), and, likely, in Japan. The Japanese species M. togakushiensis Kondo & Kobayashi, 2005 seems to be conspecific with M. middendorffi because of similar morphological patterns, small shell size (