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Currently, the parasitic and endosymbiontic fauna of Corbicula clams remain poorly studied throughout their range. Here, using samples from the Mekong basin, we describe two Symbiocloeon species new to science: Symbiocloeon corbiculinus sp. nov. and Symbiocloeon laoensis sp. nov. Our results and a review of available published data indicate that freshwater bivalve-associated mayflies are narrow host specialists, being associated with one or a few closely related species of freshwater bivalves. The bivalve-associated mayfly larvae have several specific morphological traits compared with free-living species, which include a reduction of integument chitinization and a significant reduction of the surface structures on segments. An increase in area of the respiratory surface of larval tergalia was also recorded. The possible positive and negative effects of mayflies on the clam hosts are discussed. This study is an example of the many possible hidden associations between aquatic species that remain to be described.

Established chronologies indicate a long-term ‘Hoabinhian’ hunter-gatherer occupation of Mainland Southeast Asia during the Terminal Pleistocene to Mid-Holocene (45 000–3000 years ago). Here, the authors re-examine the ‘Hoabinhian’ sequence from north-west Thailand using new radiocarbon and luminescence data from Spirit Cave, Steep Cliff Cave and Banyan Valley Cave. The results indicate that hunter-gatherers exploited this ecologically diverse region throughout the Terminal Pleistocene and the Pleistocene–Holocene transition, and into the period during which agricultural lifeways emerged in the Holocene. Hunter-gatherers did not abandon this highland region of Thailand during periods of environmental and socioeconomic change.

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.

Five new species of the terrestrial snail genus Landouria Godwin-Austen, 1918 (Camaenidae) are described from northeastern Thailand, based on shell features, radular morphology, genital anatomy, and DNA sequence data: Landouria circinata sp. nov., L. tuberculata sp. nov., L. trochomorphoides sp. nov., L. chloritoides sp. nov., and L. elegans sp. nov. These species are phylogenetically well separated from each other by mtDNA phy-logeny and COI sequence divergences of 0.073–0.156. The record of Thaitropis Schileyko, 2004 (currently synonymized with Landouria) in Thailand is re-interpreted as referring to L. diplogramma (Möllendorff, 1902) comb. nov.

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.

The Late Pleistocene archeological site of Tham Lod Rockshelter has yielded a large number of animal remains associated with a rich lithic assemblage with a Hoabinian facies. The well-preserved collection of Caprinae dental material was analyzed and attributed to three Caprinae species. The morphological and metrical analysis allowed the identification of the Sumatran serow (Capricornis sumatraensis), the Chinese goral (Naemorhedus griseus), and the Himalayan goral (N. goral). To understand the relation between the Caprinae and the prehistoric hunter-gatherers, the paleodemography of the three species was reconstructed using age estimation at the death based on tooth wear. The mortality profile revealed that the Homo sapiens hunter-gatherers adopt a generalized subsistence strategy for these preys. This new data contribute to our knowledge on the mammalian biodiversity during the Late Pleistocene in Southeast Asia and add new information about the subsistence behavior of prehistoric hunter-gatherers in northern Thailand.

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.

Muangnua arborea Tumpeesuwan & Tumpeesuwan, sp. nov., is described, based on specimens deposited in the land snail collection of Mahasarakham University, Thailand. This species is the second described in the genus Muangnua, for which colour pictures of the living semislug in natural habitats, scanning electron microscope photos of the radula, and anatomy of the mature specimens were studied and presented for the first time for this genus. Keys to genera of Southeast Asian slug-like semislugs and species of Muangnua are provided.

Sesara triodon n.sp. is described from the Phu Pha Lom limestone area in Loei, northeastern Thailand. It possesses a small and depressed–conoid, transparent shell with a shiny external surface. The aperture possesses three apertural teeth, in contrast to other Thai species, Sesara parva Solem, 1966 (two teeth) and Sesara megalodon Blanford, 1902 (four teeth). The genital system of the new species has some distinctive characters, including a vagina longer than the free oviduct, and the epiphallic retractor caecum is rounded and bulbous. The radula has 104 rather straight rows of teeth, with each row having74–81 teeth. This is the easternmost record of the genus Sesara in Thailand.http://zoobank.org/urn:lsid:zoobank.org:pub:52EF0AB6-1E17-4B96-BC6F-4257FE5FBF00

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 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.

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 (

The species in the dobsonfly genus Acanthacorydalis van der Weele, 1907 (Megaloptera: Corydalidae: Corydalinae) are some of the largest freshwater insects in the World. It is a small genus occurring only in Asia and currently comprises eight species, seven of which are restricted to the Oriental Realm (Glorioso 1981; Liu et al. 2005; Yang & Liu 2010; Cao & Liu 2013). Six species are known from China (four considered endemic), two from India, and two species occur in Vietnam (Liu et al. 2005; Yang & Liu 2010; Letardi et al. 2012). Glorioso (1981) noted that the geographical range of the genus extended from northeastern India to Vietnam. No records of Acanthacorydalis are currently available from Myanmar.

In this paper we present the first ecological data of Indochinese freshwater pearl mussel, Margaritifera laosensis populations. We also provide a comparative study of the ecology of this tropical species with populations of other Margaritiferidae. We conducted surveys in ten tributaries of the River Nam Ou (Middle Mekong Drainage, Northern Laos). Reproductively viable populations were found only in the Nam Long and Nam Pe rivers, which are two of the only three known viable populations of this species in the world. The habitats of M. laosensis include mountainous oligotrophic rivers with circumneutral pH. Optimal mesohabitats are riffles and runs with a median depth of 0.2 m and median current velocity of 0.3 ms−1. Pearl mussels were more common in gravel and fine gravel riverbed substrates. Surveys revealed 252 specimens, but only 78 (31.0%) were alive. The largest mussels observed were 110 mm in length and only 11–12 years of age. The presence of smaller-sized mussels indicates recent recruitment in both populations. The most significant threats to M. laosensis populations are harvest by local people and land development in the River Nam Ou Basin.