New freshwater mussel genus and species discovered in Anhui, China

A tiny freshwater mussel collected from a river in eastern China has turned out to belong to an entirely new genus and species, according to a taxonomic study published in the journal Zoosystematics and Evolution. The animal, named Huizhou xietianxiangi, was found in the Xinanjiang River in Xiuning County, Huangshan City, Anhui Province, and is described on the basis of both shell morphology and molecular phylogenetic analysis.

The specimens were collected in August 2025 from the Xinanjiang River at coordinates 29.5678°N, 117.9225°E, near Bingtan Village in Xikou Town. The animals were preserved in 95% ethanol and deposited at the Museum of Biology, Nanchang University in China. Researchers measured shell length, width and height with a Vernier caliper, recording a holotype with a shell length of 33.7 millimetres, a shell width of 14.7 millimetres and a shell height of 25.7 millimetres, along with two paratypes of similar size.

The new mussel is small-bodied, with a shell that the authors describe as oval, thick and solid. Its most striking feature is a zigzag sculpture that covers the entire shell surface, strengthening from the umbo toward the shell edge, and the shell is often adorned with dark green rays. The umbo is inflated and often eroded, the ligament is short and strong, and the nacre inside the shell is white to bluish-white. The incurrent and excurrent apertures bear obvious papillae arranged in a single row, and the papillae of the excurrent aperture are more than twice the size of those of the incurrent aperture, with brown pigmentation on both apertures.

To test whether the distinctive animals truly represented something unknown, the team extracted total genomic DNA from foot tissue and amplified F-type mitochondrial COI sequences using established primers. The polymerase chain reaction products were purified and sequenced on an ABI 3730XL analyzer, and the newly obtained sequences were deposited in GenBank, with accession numbers listed as in submission at the time of publication. Sequences were aligned with MAFFT v.7 using the Q-INS-i method, and pairwise distances between species were calculated in MEGA X.

For the phylogenetic work, the best-fit substitution model was selected using ModelFinder, and the researchers ran both Bayesian inference and maximum likelihood analyses, using MrBayes version 3.2.6 and IQ-TREE version 2.2 respectively. The Bayesian analysis employed two simultaneous runs with four Markov chains over 2,000,000 generations, discarding the first 25% of sampled trees as burn-in, while maximum likelihood node support was assessed with 1,000 rapid bootstrap replicates. The GTR+F+I+R4 model was selected as the best-fit model of nucleotide substitution.

The resulting molecular phylogenies showed that the subfamily Unioninae formed a monophyletic group, with bootstrap support of 85% and a Bayesian posterior probability of 0.94. More importantly for the new find, the species collected from Huangshan clustered together with Globunio mirificus, another recently described Chinese species, forming a strongly supported monophyletic clade with bootstrap support of 86% and a posterior probability of 0.92. Pairwise uncorrected COI p-distance analysis showed a genetic distance of 11% between the Huangshan species and Globunio mirificus.

That combination of molecular and morphological evidence led the authors to establish a new genus, Huizhou, within the tribe Globunionini of the subfamily Unioninae, with Huizhou xietianxiangi as its type species. The genus name derives from Huizhou, an ancient Chinese place name and historical administrative region corresponding to the area where the species was discovered. The species is named in honor of Mr. Xie Tianxiang, a conchologist who collected the specimens. The authors note that the new genus differs morphologically from Globunio, the type genus of the tribe, by lacking that genus’s diagnostic elongated-globular shell, and that the 11% COI distance between the two genera falls within the range of intergeneric divergence observed in other unionid tribes.

The tribe Globunionini itself is very new to science: it was established in 2025 and, until now, contained only a single species, Globunio mirificus. The discovery of a second member therefore provides independent support for the validity of the tribe and confirms that it is not a monotypic lineage. Like G. mirificus, the new species has a small, thick shell and lives within the Yangtze River Basin, a region that harbors a rich and endemic fauna of primary freshwater mussels with more than 70 recognized species described to date.

Despite that documented richness, the authors argue that the full diversity of the basin’s mussels remains incompletely understood, particularly among small-bodied forms, a point underscored by the recent identification of even new tribes in the region. The Yangtze basin has seen a steady stream of new taxa in recent years, and the authors conclude that a significant number of freshwater mussel species in the region are still awaiting description. Anhui Province is recognized for its rich unionid diversity, yet the present study confirms that undescribed species, particularly small-bodied or cryptic taxa, likely remain overlooked there.

There is also a conservation dimension to the find. Huizhou xietianxiangi is currently known only from the Xin’an River in Xiuning County, making its range considerably narrower than that of its relative G. mirificus and apparently endemic to Anhui Province. The authors describe this restricted range as particularly concerning, given that numerous freshwater mussel species have been reported as endangered or extinct at the time of their discovery. They urge more detailed and systematic surveys in the region to identify such hidden diversity, so that these species can be studied and given conservation priority before their habitats experience irreversible degradation. For now, the elegant zigzag-sculptured mussel of the Xinanjiang stands as both a taxonomic surprise and a reminder of how much undocumented life may persist in well-studied river systems.

Subject of Research: Taxonomic description of a new genus and species of freshwater mussel from Anhui, China, based on morphology and COI phylogenetics

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

Article References: Chen, H., Wang, W.-H., Chen, Z.-G., Xiang, H.-Q., He, Y.-M., Ouyang, S., Chu, K.-L., & Wu, X.-P. (2025). A new genus and species of freshwater mussel (Bivalvia, Unionidae) from Anhui, China. Zoosystematics and Evolution, 101(4), 2243-2250. https://doi.org/10.3897/zse.101.171070

Image Credits: AI Generated

DOI: 10.3897/zse.101.171070

Keywords: freshwater mussels, Unionidae, new species, new genus, Anhui, Yangtze River Basin, COI barcode, phylogenetics, taxonomy, Globunionini, biodiversity, conservation