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Freshwater bivalves (Bivalvia, Unionida, Unionidae) are among the most threatened groups of animals in the world. Taxonomic uncertainties pose a particular challenge due to significant intraspecific variation and apparent plasticity in shell morphology among these species, impeding efficient conservation planning and management. The species Unio szechenyii that is endemic to China has long been regarded as a synonym for Cuneopsis heudei due to the high convergence in shell morphology. The recently validated species Middendorffinaia mongolica is currently restricted to the Amur Basin and Primorye in eastern Russia. This species is classified under the tribe Middendorffinaiini of the subfamily Unioninae within the family Unionidae based on multilocus phylogeny. However, the lack of comprehensive taxonomic information and sufficient molecular phylogenetic data casts uncertainty on the validity and taxonomic status of these two species. We aim to reassess the validity of Unio szechenyii and confirm the taxonomic status of Middendorffinaia mongolica , a new record for China, by integrating taxonomy with robust mitochondrial phylogenomics. We support the validity of Unio szechenyii and propose a recombination as Cuneopsis szechenyii comb. nov. by integrating shell morphometry, soft-body anatomy and molecular evidence. By determination of the mitochondrial genome of Cuneopsis szechenyii , Cuneopsis kiangsiensis , Middendorffinaia mongolica and Pseudocuneopsis wuana , we elucidate intrageneric relationships within the genera Cuneopsis and Pseudocuneopsis. In addition, based on the updated consensus taxonomic framework including tribes and subtribes in Unioninae, mitochondrial phylogenomics strongly support the transfer of Middendorffinaia mongolica from the tribe Middendorffinaiini to the tribe Unionini and classification under the subtribe Middendorffinaiina stat. rev. ZooBank: The maternal mitochondrial genomes of Unio szechenyii , Cuneopsis kiangsiensis , Middendorffinaia mongolica and Pseudocuneopsis wuana are sequenced. The validity of Unio szechenyii , previously considered a synonym of Cuneopsis heudei , is supported by the integration of conchometry, soft-body anatomy and molecular evidence, and a recombination as Cuneopsis szechenyii comb. nov. is proposed. The intrageneric relationships within the genera Cuneopsis and Pseudocuneopsis are elucidated based on the mitochondrial phylogenomics. Middendorffinaia mongolica , a new record for China, is proposed for transfer from the tribe Middendorffinaiini to the tribe Unionini and classification under the subtribe Middendorffinaiina stat. rev. (Image credit: Ruiwen Wu.) [ABSTRACT FROM AUTHOR]

We diagnose and describe a new freshwater mussel species of the genus Inversidens, I. rentianensis sp. nov. from Jiangxi Province, China based on morphological characters and molecular data. This paper includes a morphological description and photograph of the holotype, and partial sequences of mitochondrial COI as DNA barcode data. [ABSTRACT FROM AUTHOR]

Accurate identification and precise classification of freshwater mussel species that are among the most threatened freshwater taxa in the world, play a crucial role in informing conservation and management efforts for these organisms. However, due to the variability in shell morphology, relying solely on shell characteristics for species taxonomy poses significant challenges, thereby impeding effective conservation planning and management. The freshwater mussel genus Ptychorhynchus Simpson, 1900 is one such group in need of study. We integrate molecular phylogeny, shell morphology and soft-body anatomy to examine the classification of Ptychorhynchus denserugata (Haas, 1910) and Ptychorhynchus resupinatus (von Martens, 1902). The COI barcoding data support the clustering of P. denserugata and Nodularia douglasiae within a single clade, and P. denserugata shares the diagnostic feature of the genus Nodularia , i.e. knobs or bumps on the inner mantle surface in the excurrent aperture. Therefore, by integrating molecular data and anatomical characteristics, we confirm that the nominal species P. denserugata syn. nov. is a new synonym for N. douglasiae. The multi-locus (COI + ND1 + 16S rRNA + 18S rRNA + 28S rRNA) phylogeny and mitochondrial phylogenomics support the transfer of P. resupinatus from Ptychorhynchus to the newly elevated genus Cosmopseudodon stat. rev., as Cosmopseudodon resupinatus stat. rev. that is still considered the designated type species. We also describe a new species based on integrative taxonomy, i.e. Cosmopseudodon wenshanensis sp. nov. The comprehensive understanding of the taxonomy and diversity of the revised Cosmopseudodon species, and shell heteromorphism of N. douglasiae (= P. denserugata syn. nov.), will serve as a crucial foundation for further scientific assessment and conservation strategies pertaining to these taxa. ZooBank: Ptychorhynchus resupinatus is transferred from Ptychorhynchus to a newly elevated genus Cosmopseudodon stat. rev., as Cosmopseudodon resupinatus stat. rev. Ptychorhynchus denserugata syn. nov. is confirmed as a new synonym for Nodularia douglasiae. A new species, Cosmopseudodon wenshanensis sp. nov., is described based on integrative taxonomy. (Image credit: Ruiwen Wu.) [ABSTRACT FROM AUTHOR]

Accurate phylogenetic reconstructions are crucial for comprehending the evolutionary histories, reproductive traits, and ecological habits of organisms. The subfamily Gonideinae of freshwater mussels is currently thought to include eight tribes. However, due to inadequate taxon sampling and molecular data, the assignment of the freshwater mussel genus Inversidens at the tribe level has been unstable. Additionally, the lack of phylogenetic data has hindered efforts to understand the basic biology and implementation of conservation efforts of Inversidens rentianensis, an endemic species to China. Here, we first present the complete mitochondrial genome of Inversidens rentianensis and offer a detailed description of its anatomical morphology. Based on DNA sequence data from five genes (COI, ND1, 16S rRNA, 18S rRNA, and 28S rRNA) and complete mitochondrial genomes, we investigated the phylogenetic position of Inversidens using various analytical methods. Both the concatenated five-gene and mitogenome datasets strongly supported that Inversidens classified to the tribe Gonideini in Gonideinae and formed a basal clade within the tribe Gonideini. Molecular dating analysis suggested that Inversidens originated during the mid-Cretaceous era (102.73 Mya, 95% highest posterior density HPD = 72.22 ‐ 137.03 Mya) and underwent diversification in the Late Paleogene era (37.92 Mya, 95% HPD = 20.39 ‐ 60.59 Mya). Moreover, based on the Quantitative Assessment of Species for Conservation (QASCP), Inversidens rentianensis is ranked as second priority, providing valuable insights for its management and conservation efforts. Taken together, this study provides a comprehensive understanding of the systematic position and evolutionary history of Inversidens within the currently accepted subfamily Gonideinae classification framework. These findings establish a solid foundation for future investigations on the ecology, reproductive behavior patterns, and conservation biology of this taxonomic group. [ABSTRACT FROM AUTHOR]

The Yangtze River drainage in China is among the most species rich rivers for freshwater mussels (order Unionida) on Earth with at least 68 species known. The freshwater mussels of the Yangtze River face a variety of threats with indications that species are declining in abundance and area of occupancy. This study represents the first analyses of the genetic structure and diversity for the common and widespread freshwater mussel Nodularia douglasiae based on microsatellite DNA genotypes and mitochondrial DNA sequences. Phylogenetic analysis a fragment of the COI mitochondrial gene indicated that N. douglasiae collected from across the middle and lower Yangtze River drainage are monophyletic with N. douglasiae from Japan, Russia, and South Korea. The results of the analysis of both the mtDNA and microsatellite datasets indicated that the seven collection locations of N. douglasiae in the middle and lower Yangtze River drainage showed high genetic diversity, significant genetic differentiation and genetic structure, and stable population dynamics over time. Moreover, we found that the connections among tributaries rivers and lakes in the Yangtze River drainage were important in maintaining gene flow among locations that N. douglasiae inhabits. An understanding of the genetic structure and diversity of a widespread species like N. douglasiae could be used as a surrogate to better understand the populations of other freshwater mussel species that are more rare in the Yangtze River drainage. At the same time, these results could provide a basis for the protection of genetic diversity and management of unionid mussels diversity and other aquatic organisms in the system. [ABSTRACT FROM AUTHOR]