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Sundadontina panhai Nahok, C. Tumpeesuwan & S. Tumpeesuwan,
in Nahok, Chanlabut, Tanmuangpak, Bolotov, Vikhrev, C Tumpeesuwan et S Tumpeesuwan, 2026. |
Abstract
The Mekong River basin is a globally recognized freshwater biodiversity hotspot. The most species-rich radiation of freshwater mussels in this basin belongs to the tribe Pseudodontini. This group contains numerous local endemic species that prefer small river and stream habitats with fast currents, rocky or gravel substrates, and clean water. Here, we describe Sundadontina panhai Nahok, C. Tumpeesuwan & S. Tumpeesuwan, sp. nov., a new species within this unique tribe. This species was discovered in remote tributaries of the Upper Chi River drainage, northeastern Thailand. Its taxonomic status was evaluated using an integrative approach, combining an analysis of shell morphology and mtDNA phylogeny (based on COI and 16S rRNA gene sequences). The new species differs from its congeners by a combination of unique conchological characteristics, including an elongate-ovate shell without a prominent wing, an unprojected umbo, a yellowish to dark brown periostracum, and a clearly protruding, triangular pseudocardinal tooth. All Sundadontina species are phylogenetically well-separated from each other in the mtDNA phylogeny, exhibiting a corrected COI p-distance of 2.5–16.1%. Our findings highlight that remote tributaries of the Mekong River still house undescribed endemic lineages of freshwater mussels, which are on the brink of extinction due to habitat degradation, rapid deforestation, river damming, irrigation and drainage projects, and other anthropogenic activities.
Key words Disjunct distribution, endemic freshwater mussel, habitat specialist, lotic ecosystem, phylogeny
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Maps showing the geographic distribution of the genus Sundadontina. (A) General distribution of Sundadontina species (circles) and the type locality of the new species (red star) across mainland Southeast Asia; areas outlined by a dashed line indicate historical records from vague localities that could not be precisely georeferenced. (B) Detailed sampling localities of Sundadontina panhai sp. nov. in the headwaters of the Chi River, northeastern Thailand, highlighting the type locality (red star) and additional collection sites (red circles). Maps were generated using QGIS v. 3.44 with the map base from HydroSHEDS (Lehner and Grill, 2013). (Maps: U. Chanlabut). |
Family Unionidae Rafinesque, 1820
Subfamily Gonideinae Ortmann, 1916
Tribe Pseudodontini Frierson, 1927
Subtribe Pseudodontina Frierson, 1927
(type genus: Pseudodon Gould, 1844; by original designation).
Genus Sundadontina Bolotov et al., 2020
(type species: Anodonta cumingii Lea, 1851; by original designation)
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Holotype of Sundadontina panhai sp. nov. (ZCPRU-0051). External view of (A) right valve and (B) left valve. Internal view of (C) left valve and (D) right valve. (E) dorsal view of the shell; (F) details of the pseudocardinal teeth, showing the left valve on the left-hand side and the right valve on the right-hand side. (Photos: B. Nahok) |
Sundadontina panhai Nahok, C. Tumpeesuwan & S. Tumpeesuwan, sp. nov.
Diagnosis. The shell is elongate-ovate, rather thick. The umbo is not prominent, the posterior margin is somewhat biangular, without a prominent wing. The periostracum is yellowish to dark brown, sometimes with a copper-colored tint on the posterior margin; the nacre is whitish and shining. The pseudocardinal tooth is clearly protruding and triangular. The anterior adductor muscle scar is elliptical and distinctly deep, whereas the posterior adductor muscle scar is rounded and shallower.
Etymology. The specific epithet 'panhai' is named in honor of Professor Dr. Somsak Panha, the esteemed mentor of the sixth and last authors, recognizing his pioneering leadership in the taxonomic research of land snails and freshwater bivalves in Thailand.
Benchawan Nahok, Utain Chanlabut, Kitti Tanmuangpak, Ivan N. Bolotov, Ilya V. Vikhrev, Chanidaporn Tumpeesuwan, Sakboworn Tumpeesuwan. 2026. Discover before they Disappear: A New freshwater mussel Species in the Genus
Sundadontina (Unionidae: Gonideinae: Pseudodontini) from the remote headwaters of the Chi River, Mekong Basin, northeastern Thailand.
Ecologica Montenegrina. 99; 1-18. DOI:
doi.org/10.37828/em.2026.99.1