Vietnam has the second highest diversity of freshwater mussels (Unionida) in Asia after China. The purpose of this paper is to compile an up-to-date list of the modern unionid fauna of Vietnam and its current conservation status. Unfortunately, there has been relatively little research on this fauna in Vietnam. Fifty-nine species of Unionida have been recorded from Vietnam based on literature, museum records, and our fieldwork. Fifty were assessed in the International Union for Conservation of Nature (IUCN) Red List 2016 in the IUCN categories of Critically Endangered (four species, 6.8%), Endangered (seven species, 12%), Vulnerable (one species, 1.7%), Near Threatened (two species, 3.4%), Least Concern (23 species, 39%), Data Deficient (11 species, 18.6%), and Not Evaluated (11 species, 18.6%). Considering the impacts of pollution, timbering, agriculture, and damming of rivers, research on the diversity and conservation status of freshwater mussels is very urgently needed to propose specific conservation measures for these species in Vietnam. If all taxa listed as Data Deficient are found to be threatened, with around 42% of species threatened, this fauna would be one of the most threatened freshwater molluscan faunas in Asia.

Islands have traditionally been the centre of evolutionary biological research, but the dynamics of immigration and differentiation at continental islands have not been well studied. Therefore, we focused on the Japanese archipelago, the continental islands located at the eastern end of the Eurasian continent. While the Japanese archipelago is characterised by high biodiversity and rich freshwater habitats, the origin and formation mechanisms of its freshwater organisms are not clear. In order to clarify the history of the planorbid gastropod fauna, we conducted phylogenetic analysis, divergence time estimation, ancestral state reconstruction, and lineage diversity estimations. Our analyses revealed the formation process of the planorbid fauna in the Japanese archipelago. Most lineages in the Japanese archipelago have closely related lineages on the continent, and the divergence within the Japanese lineages presumably occurred after the late Pliocene. In addition, each lineage is characterised by different phylogeographical patterns, suggesting that immigration routes from the continent to the Japanese archipelago differ among lineages. Furthermore, a regional lineage diversity plot showed that the present diversity in the Japanese archipelago potentially reflects the differentiation of lineages within the islands after the development of the Japanese archipelago. Although additional taxon sampling and genetic analysis focused on each lineage are needed, our results suggest that immigration from multiple routes just prior to the development of the Japanese archipelago and subsequent diversification within the islands are major causes of the present-day diversity of the Japanese planorbid fauna.

Freshwater shrimp of the family Atyidae De Haan, 1849 have been studied in Vietnam for more than a century. A total of 24 species of atyid shrimps from the generaCaridinaH. Milne Edwards, 1837,NeocaridinaKubo, 1938,AtyopsisChace, 1983 have been recorded from Vietnam. With 22 species, the majority are from the genusCaridina. In 2013, Karge and Klotz mentioned the occurrence of four yet undescribed species belonging toParacaridinaLiang, Guo & Tang, 1999 in Vietnam without taxonomic details.In general, studies of freshwater atyids in Vietnam are limited and most Vietnamese taxa await a taxonomic revision. The available data do not fully reflect their estimated species diversity in the country and distribution data are deficient. Here, we focus on four species of atyid shrimps from two genera, viz.Caridina cantonensisYu, 1938,C. lanceifronsYu, 1936,C. serrataStimpson, 1860 andNeocaridina palmata(Shen, 1948), all described from China and have been reported to occur in Vietnam. The previous reports on the occurrence of these species in Vietnam are largely unreliable due to taxonomic confusion. To contribute to the knowledge of these taxa, we provide the first verified distribution records of the four species in the country with some taxonomic remarks.This study shows the first taxonomically-verified distribution data of four atyid shrimp species originally described from China, but also reported from Vietnam, albeit under various species names and, in some cases, erroneously. These data allow the first meaningful discussion of the distribution in light of the reproductive strategy of these four species and, in conjunction with the taxonomic remarks, will contribute to the knowledge of these taxa. As a result of this research and data from previous studies, we now consider all four species as widespread and non-endemic, but land-locked (with a complete freshwater life cycle). In Vietnam, all four species are confined to the northern half of the country. Beyond Vietnam, we provide the first records forCaridina lanceifronsfrom southern Thailand, which suggests a major sampling gap in Indochina.

The first stygobitic species of atyid freshwater shrimps from Vietnam is described from Cuc Phuong National Park, Northern Vietnam. Caridina thachlam sp. nov. can be distinguished from its congeners by a suite of morphological characters such as strongly reduced eyes without eyestalk, short and almost unarmed rostrum and slender pereiopods. Molecular phylogenetic data from the mitochondrial cytochrome oxidase subunit I (COI) and 16S ribosomal RNA genes also support the distinctiveness of the new species from all other species that we have examined.