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| Songkhlanaia songkhramensis sp. nov. Jeratthitikul, Sutcharit & Prasankok, 2025 S. tamodienica, Songkhla Lake Basin, Thailand; S. moreleti, Tonle Sap Basin, Thailand |
Abstract
Mainland Southeast Asia, also known as Indochina, is recognized as a global biodiversity hotspot for freshwater mussels, hosting a significant number of species and exhibiting high levels of endemism. Recently, the monotypic genus Songkhlanaia was described from the Songkhla Lake Basin in southern Thailand. In this study, two additional lineages are revealed, S. moreleti comb. nov. and S. songkhramensis sp. nov., from the Mekong Basin through an integrative taxonomic approach combining morphological characters and molecular phylogenetic analyses. The multi-locus phylogenetic inference supported the monophyly of the genus and further elucidated the sister relationship between S. moreleti and the new species, and with S. tamodienica positioned as a basal lineage. Pairwise uncorrected COI p-distances among these three species also supported the species validity and ranged from 4.2% to 8.24%. Notably, S. songkhramensis sp. nov. and S. moreleti exhibit similarities in shell morphology; however, the new species can be differentiated by more robust pseudocardinal teeth. Both species are distinguishable from S. tamodienica by their approximately twice larger size, more inflated shells, and more prominent, roughened, irregular growth lines on the shell surface. Furthermore, based on the current data, these three species are recognized as endemic and are restricted to disjunct biogeographic areas in Indochina: S. tamodienica in the Songkhla Lake Basin in southern Thailand, S. moreleti in the Tonle Sap and Lower Mekong basins, and S. songkhramensis sp. nov. in the Songkhram Basin and its nearby tributaries of the Middle Mekong Basin.
Key words: Freshwater mussels, Indochina, Mekong Basin, multi-locus phylogeny, new taxa, Pseudodontini, taxonomic revision, Thailand
Family Unionidae Rafinesque, 1820
Subfamily Gonideinae Ortmann, 1916
Tribe Pseudodontini Frierson, 1927
Subtribe Pseudodontina Frierson, 1927
Genus Songkhlanaia Konopleva, Lheknim, Sriwoon, Kondakov, Vikhrev & Bolotov, 2023
Songkhlanaia Konopleva et al., 2023: 13, 14. Bolotov et al. 2023: 12.
Type species: Songkhlanaia tamodienica Konopleva, Lheknim, Sriwoon, Kondakov, Vikhrev & Bolotov in Konopleva et al. 2023 (by original designation).
Species included: Songkhlanaia currently consists of three species: S. tamodienica (type species), S. moreleti comb. nov., and S. songkhramensis sp. nov.
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| Shells of Songkhlanaia songkhramensis sp. nov. A holotype MUMNH-UNI3024 and B paratype MUMNH-UNI3023 from Prahang River, Songkhram Basin, Thailand C specimen MUMNH-UNI0925 from Songkhram River, Songkhram Basin, Thailand. |
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| Pseudocardinal teeth, left valve on the left-hand side, and right valve on the right-hand side A S. tamodienica, topotype MUMNH-UNI2956 from Tamot Stream, Songkhla Lake Basin, Thailand B S. moreleti, specimen MUMNH-UNI0301 from Phrom Hot Stream, Tonle Sap Basin, Thailand C S. songkhramensis sp. nov., holotype MUMNH-UNI3024 from Prahang River, Songkhram Basin, Thailand. Scale bars: 10 mm. |
Ekgachai Jeratthitikul, Chirasak Sutcharit and Pongpun Prasankok. 2025. An integrative approach to A Revision of the freshwater mussel Genus Songkhlanaia (Bivalvia, Unionidae), with the Description of A New Species. ZooKeys. 1224: 187-209. DOI: doi.org/10.3897/zookeys.1224.140549
