Lili Liu

The family Unionidae is a diverse and ecologically significant group of freshwater invertebrates, playing a keystone role in the energy flow and nutrient cycling in aquatic ecosystems. A recent taxonomic revision of the East Asian endemic subtribe Cristariina within Unionidae has revealed its division into seven genera. As an important part of East Asia, China harbours an exceptionally diverse and highly unique fauna of freshwater mussels. However, a comprehensive understanding of species diversity and phylogenetic relationships of Cristariina remains elusive due to inadequate sampling in previous studies, particularly in China. Here, we conducted comprehensive taxonomic and mitogenomic phylogenetic analyses of Cristariina based on extensive sampling across 17 provinces in China. The COI sequences of Cristariina in GenBank were thoroughly examined, and combined with the sequences obtained from this study, a total of 33 monophyletic groups were identified. By integrating molecular data and morphological characteristics, we describe a new genus and species: Acudonta baitiaoensisgen. nov., sp. nov., as well as a newly recorded species for China (Cristaria truncata). Additionally, we confirm that the nominal species Anemina euscaphyssyn. nov., Anemina flumineasyn. nov. and Anemina globosulasyn. nov. are junior synonyms of Anemina arcaeformis through integrative taxonomy. Mitogenomic phylogeny establishes the following robust phylogenetic framework at the generic level within Cristariina: ((((Sinanodonta + Acudontagen. nov.) + (Beringiana + Pletholophus)) + ((Anemina + Buldowskia) + Amuranodonta)) + Cristaria). Besides Sinanodonta and Cristaria, the distribution of other genera of Cristariina in China exhibits distinct faunal regions of endemism. ZooBank: urn:lsid:zoobank.org:pub:30E44DEB-3CCD-47F7-A2B2-3FA851BE434E

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 szechenyiicomb. 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: urn:lsid:zoobank.org:pub:820589D5-0100-4195-B92B-1E1005384B9B

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: urn:lsid:zoobank.org:pub:E48968B1-DF0F-42AD-8F31-B8C95F23CE57

In this study, we present a new species of freshwater mussel in the genus PostolataDai et al., 2023, from Guangxi Province, China, by integrating morphological, anatomical, and molecular data. Postolata longjiangensis Liu & Wu, sp. nov. is distinguished from its congener (i.e., Postolata guangxiensis) by its shell shape, beak position, surface sculpture, nacre color, and hinge structure. Molecular species delimitation results based on the mitochondrial COI gene support the separation of Postolata longjiangensis Liu & Wu, sp. nov. from its congener. The multi-locus (COI + 16S rRNA + 28S rRNA) phylogeny reveals that this species forms the sister lineage to Postolata guangxiensis in the tribe Gonideini.

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 Mya) and underwent diversification in the Late Paleogene era (37.92 Mya, 95% 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.

A new species of freshwater mussel belonging to the genus Pseudocuneopsis, namely Pseudocuneopsis wuanasp. nov., is diagnosed and described from Guangxi Province, China. This paper provides a detailed shell morphological description, soft-body anatomical characteristics, and partial sequences of mitochondrial COI as DNA barcode data for the novel species. The new species can be distinguished from its congeners (Pseudocuneopsis sichuanensis, P. yangshuoensis, and P. capitata) by shell shape, beak position, and surface sculpture. Phylogenetic analyses based on the mitochondrial COI gene reveal that Pseudocuneopsis wuanasp. nov. forms a sister group with P. yangshuoensis and exhibits an interspecific genetic distance of 5.1%. Therefore, we provide robust morphological and molecular evidence to support the validity of this new species.

Cyrenoidea is a superfamily of bivalves (Bivalvia: Imparidentia) currently comprising three families (Cyrenidae, Cyrenoididae and Glauconomidae). The superfamily is widely distributed in marine, brackish and freshwater environments, with an estimated 60 or more living species. Recent phylogenetic results have confirmed the monophyly of Cyrenoidea and placement in Venerida. Nevertheless, a comprehensive phylogenetic analysis of Cyrenoidea remains elusive and the phylogeny is unresolved due to inadequate sampling in previous studies. Moreover, the taxonomy and delimitation of most species, originally based on shell morphology, have not yet been tested with molecular data. Here, we constructed three molecular datasets by sequencing three markers (COI + 16S rRNA + 28S rRNA) and complete mitogenomes for Geloina coaxans (Gmelin, 1791) and Glauconome virens (Linnaeus, 1767). COI barcoding clarifies the validity of Geloina coaxans and Geloina erosa that have been subject to controversy regarding synonymy. Additionally, the barcoding supports the existence of multiple cryptic species within the Geloina expansa complex. A multi-locus dataset (COI + 16S rRNA + 28S rRNA) provides the most comprehensive phylogeny of all eight recognised genera of Cyrenoidea to date. Phylogenetic results indicate that the currently recognised family Cyrenidae is polyphyletic. The type species Geloina coaxans, Cyanocyclas limosa (Maton, 1811) and Polymesoda caroliniana (Bosc, 1801) that have long been classified within the family Cyrenidae based on shell morphology, have a closer relationship with Cyrenoida floridana Dall, 1896 than with other Cyrenidae. Therefore we transfer the genera Geloina, Cyanocyclas and Polymesoda from the family Cyrenidae to the family Cyrenoididae. The mitochondrial phylogenomics further support the family-level relationships in Cyrenoidea obtained from the three-gene analyses, confirming that the newly defined Cyrenoididae is closely related to Glauconomidae as the sister group. We observed a novel gene arrangement in Glauconome virens, the first report on the mitogenome of the family Glauconomidae, by comparing gene arrangements. Three patterns of gene rearrangement identified in Cyrenoidea are shared by the families Glauconomidae, Cyrenoididae and Cyrenidae, suggesting that gene arrangements can be a valuable tool for phylogenetic studies.