Songkhlanaia Konopleva, Lheknim, Sriwoon, Kondakov, Vikhrev & Bolotov 2023

GenusSongkhlanaiaKonopleva, 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. Diagnosis. Shell medium to large, rectangular or subrhomboidal, rather compressed to inflated. Anteriorly constricted, dorsal margin straight or slightly curved, slightly elevated posteriorly. One or two folds on posterior slope. Shell surface with fine or irregular growth lines, roughened on posterior slope or border of shell. One pseudocardinal tooth on each valve; lateral teeth obsolete. Distribution. Endemic to Indochina, including Songkhla Lake Basin, Tonle Sap Basin, and Middle to Lower Mekong basins. Comments. Songkhlanaia is represented in multi-locus phylogenetic analyses as a distinct clade among the Pseudodontini genera (Fig. 1). Morphologically, its rectangular or overall subrhomboidal shape outline also makes Songkhlanaia easily distinguishable from other genera that have somewhat narrow and elongate shells: Bineurus Simpson, 1900, Isannaia Jeratthitikul et al., 2024, Namkongnaia Jeratthitikul et al., 2021, and Pilsbryoconcha Simpson, 1900 (Jeratthitikul et al. 2021 b, 2024; Konopleva et al. 2021; Bolotov et al. 2023). Although members of Songkhlanaia possess rather short and high shell outlines which resemble those of the genera Indopseudodon Prashad, 1922, Lannanaia Jeratthitikul et al., 2024, Nyeinchanconcha Bolotov et al., 2020, Pseudodon Gould, 1844, Sundadontina Bolotov et al., 2020, and Thaiconcha Bolotov et al., 2020, the unique roughened and irregular growth lines on the outer shell surface (which are fine or less developed growth lines in S. tamodienica) make it easily distinguishable from these genera (Bolotov et al. 2020, 2023; Konopleva et al. 2021; Jeratthitikul et al. 2024). Members of Songkhlanaia are likely the largest freshwater mussels in the tribe Pseudodontini recorded to date. The largest specimen examined herein is S. moreleti (MUMNH - UNI 0301; shell length 121.7 mm) from Srakeo, Thailand. The syntype has a shell length of 123 mm (Crosse and Fischer 1876) and a specimen from Cambodia examined by Simpson (1914) reached 124 mm.