Integrative Taxonomic Reappraisal and Evolutionary Biogeography of the Most Diverse Freshwater Mussel Clade from Southeast Asia (Pseudodontini)

Abstract

Freshwater mussels belonging to the tribe Pseudodontini (Bivalvia: Unionidae: Gonideinae) play a keystone role in riverine and lacustrine environments throughout Southeast Asia. Many of them are narrowly endemic and habitat specialists, which need special conservation efforts. Unfortunately, the systematics of this group is rather poorly understood. Here, we show that Pseudodon inoscularis, the type species of the genus Pseudodon, belongs to the eastern clade of the tribe (Southeast Asia, east of the Salween Basin), and, more certainly, clusters with members of the genus Monodontina. Hence, the latter genus becomes a synonym of Pseudodon, while the subtribe Pseudodontina (=Pilsbryoconchina syn. nov.) should be used as a name for the eastern clade. In turn, the genus Indopseudodon stat. rev. and the subtribe Indopseudodontina subtr. nov. must be applied as valid names for the western clade of the Pseudodontini (Ayeyarwady to Salween). We present a revision of the genus Indopseudodon with an updated synonymy and a description of a new species, I. indawgyiensis sp. nov. We also link four species-level genetic lineages from the Mekong to available taxonomic names in the genera Pseudodon and Sundadontina (Pseudodon cambodjensis, P. vagulus, Sundadontina harmandi, and S. sulcata). Based on morphological features, we revise the taxonomic position of several recent and fossil species that were traditionally placed in the Pseudodontini and transfer them to the genera Parvasolenaia, Pseudodontopsis, Ptychorhynchus, Simpsonasus nom. nov. (a new name for Nasus Simpson, 1900) (Gonideinae: Gonideini), Pseudobaphia (Unioninae: Unionini), Balwantia and Lamellidens (Parreysiinae: Lamellidentini).

An alarming tendency towards freshwater mussel misidentification in scientific works may bias endangered and invasive species management

“…The geographical summary and checklists of species by subregions in this database (https://mussel-project.uwsp.edu/fmuotwaolcb/geography_summary.html) are a very useful tool for anyone who wants to identify freshwater mussel samples from a particular area. Comparative morphological analyses of sampled specimens should focus on the differences in shell shape, umbo position, sculpture, hinge structure and development of muscle attachment scars (Bolotov et al, 2023). In addition, MolluscaBase (https://molluscabase.org) may be used as a reliable source of updated taxonomic information on freshwater bivalves.…”

“…Among the available molecular genetic markers, the mitochondrial cytochrome c oxidase subunit I (COI) barcode fragment is recommended for species-level identification. Numerous COI sequences of freshwater mussels are already available in global DNA depositories (Bolotov et al, 2023;Bolotov, Pasupuleti, et al, 2022;Lopes-Lima al., 2020;Pfeiffer et al, 2021), and hyperlinks to the reference sequences of each genetically confirmed species in GenBank are given in the MUSSELp database (Graf & Cummings, 2023). In addition, there is also a suite of RFLP-based molecular identification keys for unionids, which can be used with low effort and cost (Zieritz et al, 2012).…”