A new genus and species of freshwater mussel (Bivalvia, Unionidae) from Anhui, China

A new genus and species of freshwater mussel (Bivalvia, Unionidae) from Anhui, China Hui Chen1, Wen-Hao Wang1, Zhong-Guang Chen1, Hong-Quan Xiang2, Yue-Ming He3, Shan Ouyang1, Ke-Lin Chu4, Xiao-Ping Wu1 1 School of Life Sciences, Nanchang University, Nanchang, 330031, China 2 Department of Animal Science, Yuxi Agriculture Vocation-Technical College, Yuxi, 653106, China 3 College of Engineering and Technology, Tianjin Agricultural University, Tianjin, 300384, China 4 Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing 210042, China https://zoobank.org/A8F7B4D9-C570-4BDD-B2C3-00A85E67A390 Corresponding authors: Xiao-Ping Wu ([email protected]); Ke-Lin Chu ([email protected]) Academic editor: Le-Jia Zhang ♦ Received 4 September 2025 ♦ Accepted 7 November 2025 ♦ Published 18 November 2025 Abstract The middle and lower reaches of the Yangtze River host a highly diverse Unionidae fauna. Herein, a new genus and species of freshwater mussel, Huizhou xietianxiangi H. Chen, Z.-G. Chen, H.-Q. Xiang, Y.-M. He & X.-P. Wu, gen. et sp. nov., is described from Huangshan City, Anhui Province, based on comparative morphological and molecular phylogenetic evidence. The new taxon is distinguished by a unique set of shell characteristics, including an oval shape, a zigzag sculpture covering the entire surface, and frequent adornment with elegant dark green rays. These distinct morphological features, coupled with significant genetic differentiation, robustly support its establishment as a new genus and species. Key Words Globunionini, Mollusca, phylogeny, taxonomy, Yangtze River Basin Introduction The Yangtze River Basin in China harbors a rich and endemic fauna of primary freshwater mussels, with more than 70 recognized species described to date (He and Zhuang 2013; Graf and Cummings 2021; Guo 2022; Dai et al. 2025). Recent extensive surveys and taxonomic studies have led to the continual discovery of new taxa (Chen et al. 2023; Dai et al. 2023, 2024a, b; Chen et al. 2025). Despite the numerous endemic species already documented, their full diversity remains incompletely understood, particularly among small-bodied forms, with even new tribes being identified (Dai et al. 2025). These findings indicate that a significant number of freshwater mussel species in the region have yet to be described. In this study, researchers collected freshwater mussel specimens with distinctive shell morphology from Huangshan City, Anhui Province, China, which did not match any known species. Based on integrated morphological and molecular phylogenetic analyses, we describe it here as a new genus and new species within the subfamily Unioninae Rafinesque, 1820: Huizhou xietianxiangi sp. nov. This discovery further enriches the known freshwater mussel diversity of the Yangtze River Basin, particularly among the tiny fauna. Materials and methods Specimen sampling and morphological observations Freshwater mussels were collected in the Xinanjiang River (29.5678°N, 117.9225°E), Bingtan Village, Xikou Zoosyst. Evol. 101 (4) 2025, 2243–2250|DOI 10.3897/zse.101.171070 Copyright Chen, H. et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. zse.pensoft.net Chen, H. et al.: New genus and species of freshwater mussels 2244 Town, Xiuning County, Huangshan City, Anhui Province, China, in August 2025 (Fig. 1). The specimens were preserved in 95% ethanol and deposited at the Museum of Biology, Nanchang University (NCUMB), China. A Vernier caliper was used to measure shell length (L), shell width (W), and shell height (H). DNA extraction, PCR, sequencing, and phylogenetic analyses Total genomic DNA was extracted from foot tissues using the TIANamp Marine Animals DNA Kit (Tiangen Biotech) following the manufacturer’s protocol. F-type mitochondrial COI sequences were amplified using primers LCO22me2 (GGTCAACAAAYCATAARGATATTGG) and HCO700dy2 (TCAGGGTGACCAAAAAAYCA) (Walker et al. 2007). Polymerase chain reaction (PCR) amplifications of COI were performed in a final 25 μL reaction mixture containing 1 μL of template DNA, 1 μL of each primer, 12.5 μL of Green Taq Mix (Vazyme, China), and 9.5 μL of ddH2O. Thermal cycling began with one cycle at 98 °C for 10 s, followed by 35 cycles of denaturation at 94 °C for 1 min, annealing at 50 °C for 1 min, and extension at 72 °C for 1 min, with a final extension at 72 °C for 7 min. The PCR products were purified and sequenced using an ABI 3730XL analyzer. The newly obtained sequences were deposited in GenBank (Table 1). Sequences were aligned using MAFFT v.7 based on the Q-INS-i method (Katoh et al. 2019). Pairwise distances between species were calculated using MEGA X (Kumar et al. 2018). The best substitution model was selected usFigure 1. Collection sites of Huizhou xietianxiangi gen. et sp. nov. The gold star indicates the type locality. Zoosyst. Evol. 101 (4) 2025, 2243–2250 zse.pensoft.net 2245 ing the corrected Bayesian Information Criterion (BIC) in MODELFINDER v.2.2.0 (Kalyaanamoorthy et al. 2017). Bayesian inference (BI) and maximum likelihood (ML) analyses were performed using MrBayes (ver. 3.2.6; Ronquist et al. 2012) and IQ-TREE (ver. 2.2; Minh et al. 2020), respectively, with reference to the selected model of sequence evolution. For Bayesian analysis, two runs were performed simultaneously with four Markov chains starting from a random tree. Bayesian posterior probabilities (BPPs) of nodes were determined using Metropolis-coupled Markov chains (one cold chain) for 2,000,000 generations, with sampling every 1000 generations. The first 25% of sampled trees were discarded as burn-in when the standard deviation of split frequencies between the two runs was less than 0.01; the remaining trees were then used to create a 50% majority-rule consensus tree and to estimate BPPs. Node support for maximum likelihood analysis was determined using 1000 rapid bootstrap (BS) replicates. Results The GTR+F+I+R4 model was selected as the best-fit model of nucleotide substitution by the AIC criterion. Molecular phylogenies based on BI and ML analyses Table 1. GenBank accession numbers of the COI sequences used in this study. Species Locality Accession number Huizhou xietianxiangi gen. et sp. nov. Xiuning, Huangshan, Anhui, China In submission Huizhou xietianxiangi gen. et sp. nov. Xiuning, Huangshan, Anhui, China In submission Globunio mirificus Chen, Dai, Huang & Wu, 2025 Nanchang, Jiangxi, China PV368604 Globunio mirificus Chen, Dai, Huang & Wu, 2025 Nanchang, Jiangxi, China PV368605 Diaurora aurorea (Heude, 1883) Ji’an, Jiangxi, China OQ829360 Acuticosta chinensis (Lea, 1868) Jiangxi, China MG462921 Schistodesmus lampreyanus (Baird & Adams, 1867) Jiangxi, China MG463037 Schistodesmus lampreyanus (Baird & Adams, 1867) Hunan, China MG463043 Schistodesmus spinosus (Simpson, 1900) Jiangxi, China MG463046 Unio pictorum (Linnaeus, 1758) Europe KC429109 Unio crassus Philipsson, 1788 Poland KY290446 Tchangsinaia piscicula (Heude, 1874) Jiangxi, China MG462977 Cuneopsis celtiformis (Heude, 1874) Jiangxi, China MG462964 Cuneopsis heudei (Heude, 1874) Jiangxi, China MG462970 Aculamprotula fibrosa (Heude, 1877) Jiangxi, China MG462909 Nodularia douglasiae (Gray, 1833) China KX822653 Nodularia breviconcha Lee, Kim, Bogan & Kondo, 2020 South Korea MT020662 Inversiunio yanagawensis (Kondo, 1982) Japan MT020654 Inversiunio reinianus (Kobelt, 1879) Japan MT020657 Pseudocuneopsis sichuanensis Huang, Dai, Chen & Wu, 2022 Sichuan, China MZ540966 Pseudocuneopsis capitata (Heude, 1874) Anhui, China NC042469 Alasmidonta marginata Say, 1818 U.S. AF156502 Lasmigona compressa (Lea, 1829) U.S. AF156503 Anodonta anatina (Linnaeus, 1758) Russia KX822632 Pseudanodonta complanata (Rossmässler, 1835) Ukraine KX822661 Lanceolaria gladiola (Heude, 1877) Jiangxi, China MG463007 Lanceolaria oxyrhyncha (Martens, 1861) Japan MT020648 Cristaria plicata (Leach, 1814) Jiangxi, China MG462956 Lepidodesma languilati (Heude, 1874) Jiangxi, China MG463015 Sinanodonta woodiana (Lea, 1834) China KX822668 Beringiana beringiana (Middendorff, 1851) Japan MT020557 Pletholophus tenuis (Gray, 1833) Vietnam KX822658 Anemina arcaeformis (Heude, 1877) Jiangxi, China MG462936 Amuranodonta kijaensis Moskvicheva, 1973 Russia MK574204 Coelatura aegyptiaca (Cailliaud, 1823) Egypt KJ081162 Indonaia andersoniana (Nevill, 1877) Myanmar MF352275 Parreysia nagpoorensis (Lea, 1860) India JQ861229 Pronodularia japanensis (Lea, 1859 Japan LC505454 Lamprotula leaii (Gray, 1833) Jiangxi, China MG462996 Lampsilis siliquoidea (Barnes, 1823) U.S. MH560773 Quadrula quadrula (Rafinesque, 1820) U.S. HM230409 Margaritifera dahurica (Middendorff, 1850) Russia KJ161516 Gibbosula rochechouartii (Heude, 1875) Jiangxi, China MG463022 zse.pensoft.net Chen, H. et al.: New genus and species of freshwater mussels 2246 Figure 2. Maximum likelihood tree inferred from COI gene sequences. 0.05 Schistodesmus lampreyanus Cuneopsis heudei Aculamprotula fibrosa Lepidodesma languilati Pseudocuneopsis sichuanensis Amuranodonta kijaensis Pseudanodonta complanata Acuticosta chinensis Lasmigona compressa Cuneopsis celtiformis Inversiunio yanagawensis Sinanodonta woodiana Huizhou xietianxiangi gen. & sp. nov. Globunio mirificus Nodularia breviconcha Lamprotula leaii Pletholophus tenuis Tchangsinaia piscicula Anemina arcaeformis Huizhou xietianxiangi gen. & sp. nov. Quadrula quadrula Margaritifera dahurica Pseudocuneopsis capitata Nodularia douglasiae Pronodularia japanensis Indonaia andersoniana Unio pictorum Lanceolaria gladiola Inversiunio reinianus Schistodesmus lampreyanus Parreysia corrugata Beringiana beringiana Alasmidonta marginata Globunio mirificus Schistodesmus spinosus Lampsilis siliquoidea Cristaria plicata Anodonta anatina Lanceolaria oxyrhyncha Gibbosula rochechouartii Diaurora aurorea Unio crassus Coelatura aegyptiaca 97 99 100 100 60 100 100 50 100 44 100 99 66 55 38 100 99 57 67 100 100 100 93 90 95 61 99 92 74 99 78 99 49 85 86 79 77 42 92 46 100 Unioninae Parreysiinae Ambleminae Gonideinae outgroups Unionidae Margaritiferidae showed that the subfamily Unioninae formed a monophyletic group (BS = 85%, BPP = 0.94). The species collected from Huangshan, Anhui, China, together with Globunio mirificus Chen, Dai, Huang & Wu, 2025, formed a strongly supported monophyletic clade (BS = 86%, BPP = 0.92) (Figs 2, 3). Pairwise uncorrected COI p-distance analysis demonstrated a genetic distance of 11% between this species and Globunio mirificus. These distances, as well as the distinct morphological characteristics, provide compelling evidence for its classification as a new genus and species, Huizhou xietianxiangi sp. nov., in the tribe Globunionini. Zoosyst. Evol. 101 (4) 2025, 2243–2250 zse.pensoft.net 2247 Figure 3. Bayesian inference tree inferred from COI gene sequences. 0.2 Schistodesmus lampreyanus Nodularia breviconcha Indonaia andersoniana Schistodesmus lampreyanus Pletholophus tenuis Acuticosta chinensis Globunio mirificus Schistodesmus spinosus Gibbosula rochechouartii Cuneopsis celtiformis Anodonta anatina Beringiana beringiana Margaritifera dahurica Sinanodonta woodiana Parreysia corrugata Nodularia douglasiae Pseudocuneopsis sichuanensis Coelatura aegyptiaca Inversiunio reinianus Huizhou xietianxiangi gen. & sp. nov. Unio crassus Aculamprotula fibrosa Cristaria plicata Diaurora aurorea Tchangsinaia piscicula Globunio mirificus Lepidodesma languilati Inversiunio yanagawensis Lasmigona compressa Cuneopsis heudei Alasmidonta marginata Lamprotula leaii Pseudanodonta complanata Quadrula quadrula Lampsilis siliquoidea Pronodularia japanensis Unio pictorum Amuranodonta kijaensis Lanceolaria oxyrhyncha Anemina arcaeformis Lanceolaria gladiola Huizhou xietianxiangi gen. & sp. nov. Pseudocuneopsis capitata 1 1 0.41 1 0.88 0.32 0.68 0.39 0.92 0.63 1 1 0.91 0.51 0.64 1 1 1 0.29 0.99 0.14 0.43 1 0.26 1 0.75 0.98 0.66 0.93 0.6 1 0.64 0.9 0.98 0.94 0.77 0.56 0.94 1 0.35 1 Margaritiferidae Ambleminae Gonideinae Parreysiinae Unioninae Unionidae outgroups Systematics Family Unionidae Rafinesque, 1820 Subfamily Unioninae Rafinesque, 1820 Tribe Globunionini Y.-T. Dai, Z.-G. Chen, X.- C. Huang & X.-P. Wu, 2025 Genus Huizhou H. Chen, Z.-G. Chen, H.-Q. Xiang, Y.-M. He & X.-P. Wu, gen. nov. https://zoobank.org/0486F794-ADEB-46B5-8A00-94DBD10A0E5A Type species. Huizhou xietianxiangi H. Chen, Z.-G. Chen, H.-Q. Xiang, Y.-M. He & X.-P. Wu, gen. et sp. nov. (Fig. 4). Diagnosis. Shell small-sized, oval, thick, solid; with a zigzag sculpture covering the entire surface, often adorned with elegant dark green rays. Umbo inflated, often eroded. Incurrent aperture and excurrent aperture obvious papillae arranged in one row, excurrent aperture papillae are more than twice the size of the incurrent aperture. Etymology. The name of this genus originates from the ancient Chinese place name Huizhou, which was an administrative region in Chinese history. The ancient name of the place where this species was discovered. Vernacular name. 徽州蚌 (hui zhou bang). English common name: Huizhou Mussel. Remarks. The establishment of the new genus Huizhou is justified by congruent evidence from morphology and molecular phylogeny. It differs morphologically from the type genus Globunio of the tribe Globunionini by lacking the diagnostic elongated-globular shell. Phylogenetically, zse.pensoft.net Chen, H. et al.: New genus and species of freshwater mussels 2248 Figure 4. Huizhou xietianxiangi gen. et sp. nov. A–E. Holotype, NCUAH250801; F–H. Paratype, NCUAH250802; I–L. Paratype, NCUAH250803; M, N. Hinge structure of left and right valves; O. Anatomical features, p ia, papillae in incurrent aperture; p exa, papillae in excurrent aperture. Scale bars: 10 mm (A–L), 1 mm (M, N), 1 mm (O). the two genera form distinct, strongly supported lineages with a considerable genetic distance (11% for COI), which falls within the range of intergeneric divergence observed in other unionid tribes. This combination of marked morphological discontinuity and significant genetic differentiation provides compelling evidence for their separation at the generic level. Huizhou xietianxiangi H. Chen, Z.-G. Chen, H.-Q. Xiang, Y.-M. He & X.-P. Wu, sp. nov. https://zoobank.org/2DF41693-B63D-44BD-BE42-6AF3A2625A02 Material examined. Holotype: NCUAH250801, shell length 33.7 mm, shell width 14.7 mm, shell height 25.7 mm (Fig. 4A), Xinanjiang River, Bingtan Village, Xikou Town, Xiuning County, Huangshan City, Anhui Province, China, 29.5678°N, 117.9225°E, in August 2025. Paratypes: 2 specimens, NCUAH250802, 03; shell length 35.2, 33.5 mm; shell width 27.5, 25.1 mm; shell height 15.1, 13.8 mm; locality and habitat same as holotype. Diagnosis. Same as the genus. Description. Shell small-sized, oval, thick, solid; with a zigzag sculpture covering the entire surface but strengthening from umbo to edge, often adorned with elegant dark green rays. Umbo inflated, often eroded. Ligament short and strong. Mantle muscle scars obvious. Anterior adductor muscle scars oval, deep; posterior adductor muscle scars oval, shallow and smooth (Fig. 4A–L). Left valve with two pseudocardinal teeth, equal height; anterior pseudocardinal tooth of the right valve well developed, posterior pseudocardinal tooth reduced. Lateral teeth of both valves thick (Fig. 4M, N). Nacre white bluish-white. Incurrent aperture and excurrent apertures obvious papillae arranged in one row, excurrent aperture papillae are more than twice the size of the incurrent aperture, both aperture with brown pigmentation (Fig. 4O). Zoosyst. Evol. 101 (4) 2025, 2243–2250 zse.pensoft.net 2249 Figure 5. Habitats and live animals of Huizhou xietianxiangi gen. et sp. nov. Etymology. The name of this species is in honor of Mr. Xie Tianxiang, a conchologist who collected the specimens. Vernacular name. 谢氏徽州蚌 (Xie shi hui zhou bang). English common name: Xie’s Huizhou Mussel. Habitat and distribution. This species is currently only known to be distributed in the Xin’an River in Xiuning County, Huangshan City, Anhui Province (Figs 1, 5). Discussion The tribe Globunionini was recently established and previously included only Globunio mirificus (see Dai et al. 2025). In this study, through a combination of morphological and molecular phylogenetic analyses, we describe a new genus and species, Huizhou xietianxiangi gen. et sp. nov., from the Xinanjiang River in Anhui Province. The discovery of this second species provides critical independent support for the validity of the tribe Globunionini and confirms that it is not a monotypic lineage. This finding significantly enriches species diversity and enhances our understanding of the tribe’s evolutionary history. Similar to G. mirificus, H. xietianxiangi gen. et sp. nov. possesses a small and thick shell and occurs within the Yangtze River Basin (Dai et al. 2025). However, our findings reveal that H. xietianxiangi exhibits a considerably narrower distribution and is currently endemic to Anhui Province. This restricted range is particularly concerning given that numerous freshwater mussel species have been reported as endangered or extinct at the time of their discovery (Xiang et al. 2024, 2025). Although Anhui Province is recognized for its rich unionid diversity, the present study confirms that undescribed species, particularly small-bodied or cryptic taxa, likely remain overlooked. Therefore, we urge more detailed and systematic surveys in this region to identify such hidden diversity, ensuring that these species can be studied and afforded conservation priority before their habitats experience irreversible degradation. Acknowledgments We thank Tianxiang Xie and Boyu Wang for their valuable contributions to specimen collection in this study. We are grateful to the editor, Lejia Zhang, and the reviewers, Ivan N. Bolotov and Arthur Bogan, for their insightful suggestions and constructive comments, which have greatly improved the quality of this manuscript. 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