Ecologica Montenegrina 41: 73-83 (2021) This journal is available online at: www.biotaxa.org/em http://dx.doi.org/10.37828/em.2021.41.11 https://zoobank.org/urn:lsid:zoobank.org:pub:2ED2B90D-4BF2-4384-ABE2-630F76A1AC54 Nominal taxa of freshwater Mollusca from Southeast Asia described by Dr. Nguyen N. Thach: A brief overview with new synonyms and fixation of a publication date IVAN N. BOLOTOV1,2, EKATERINA S. KONOPLEVA1,2,*, ILYA V. VIKHREV1,2, MIKHAIL Y. GOFAROV1,2, MANUEL LOPES-LIMA3,4,5, ARTHUR E. BOGAN6, ZAU LUNN7, NYEIN CHAN7, THAN WIN8, OLGA V. AKSENOVA1,2, ALENA A. TOMILOVA1, KITTI TANMUANGPAK9, SAKBOWORN TUMPEESUWAN10 & ALEXANDER V. KONDAKOV1,2 1N. Laverov Federal Center for Integrated Arctic Research of the Ural Branch of the Russian Academy of Sciences, Northern Dvina Emb. 23, 163000 Arkhangelsk, Russia. 2Northern Arctic Federal University, Northern Dvina Emb. 17, 163002 Arkhangelsk, Russia. 3CIBIO/InBIO – Research Center in Biodiversity and Genetic Resources, University of Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas 7, 4485-661 Vairão, Portugal. 4CIIMAR/CIMAR – Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Terminal de Cruzeiros do Porto de Leixões, Avenida General Norton de Matos, S/N, 4450-208 Matosinhos, Portugal. 5SSC/IUCN – Mollusc Specialist Group, Species Survival Commission, International Union for Conservation of Nature, c/o The David Attenborough Building, Pembroke Street, CB2 3QZ Cambridge, United Kingdom. 6North Carolina Museum of Natural Sciences, 11 West Jones St., Raleigh, NC 27601, United States of America 7Fauna & Flora International – Myanmar Programme, Yangon, Myanmar. 8 Department of Zoology, Dawei University, Dawei, Tanintharyi Region, Myanmar. 9Department of Science, Faculty of Science and Technology, Loei Rajabhat University, Loei, Thailand. 10Department of Biology, Faculty of Science, Mahasarakham University, Maha Sarakham, Thailand. *Corresponding author: [email protected] Received: 27 February 2021│ Accepted by V. Pešić: 21 April 2021 │ Published online: 26 April 2021. In this correspondence, we present a summary of taxonomic names of freshwater Mollusca introduced by Dr. Nguyen N. Thach, an enthusiastic and productive malacologist from Vietnam. We show that this researcher described one new genus and 12 new nominal species of freshwater molluscs from Southeast Asia. Two of these nominal species, Sinanodonta hunganhi Thach, 2016 and Lanceolaria bogani Thach, 2016 (Bivalvia: Unionidae), were already considered junior synonyms of S. jourdyi (Morlet, 1886) and L. fruhstorferi (Dautzenberg, 1900), respectively (Do et al. 2018; Đặng and Hố 2019). Here, we propose one more synonym for the invasive Golden Apple Snail as follows: Pomacea canaliculata (Lamarck, 1822) [=Pomacea thachi Huber in Thach, 2020 syn. nov.] (Gastropoda: Ampullariidae). Furthermore, we establish the formal synonymy for the following taxa: Taia Annandale, 1918 [=Boganmargarya Thach, 2018 syn. nov.]; Taia shanensis (Kobelt, 1909) [=Boganmargarya huberi Thach, 2018 syn. nov.] (Gastropoda: Viviparidae); Brotia henriettae (Gray in Griffith & Pidgeon, 1833) [=Brotia frankhuberi Thach, 2020 syn. nov.; Brotia bogani Thach & Huber in Thach, 2020 syn. nov.] (Gastropoda: Pachychilidae); Pila pesmei (Morlet, 1889) Ecologica Montenegrina, 41, 2021, 73-83 FRESHWATER MOLLUSCA DESCRIBED BY DR. NGUYEN N. THACH [=Pila huberi Thach, 2020 syn. nov.] (Gastropoda: Ampullariidae); and Paludomus andersoniana Nevill, 1877 [=Paludomus huberi Thach, 2020 syn. nov.] (Gastropoda: Paludomidae). Additionally, four nominal species are treated here as taxa inquirenda: Melanoides thachi Huber in Thach, 2020 (Gastropoda: Thiaridae), Trochoita frankohleri Thach & Huber in Thach, 2020 (Gastropoda: Viviparidae), Paracrostoma huberi Thach, 2018 (Gastropoda: Pachychilidae), and Pseudodon artbogani Thach & Huber in Thach, 2020 (Bivalvia: Unionidae). We also show that the publication date written on the title page of the book “New Shells of South Asia. Volume 2” (Thach, 2020a) is a bit misleading and that this book appeared in the printed form on 23 June 2020. The latter date is fixed here as the date of availability of taxonomic names introduced in this work. Finally, we present an annotated checklist of freshwater Mollusca described by N. N. Thach with approximate coordinates of the type localities and reference to corresponding river drainage basins. Nguyen N. Thach is a productive amateur malacologist, who initially published several faunal reviews and guides on Mollusca from Vietnam (Thach 2005, 2007, 2012). These works were considered an important source of taxonomic and distributional information on the regional malacofauna, at least for freshwater taxa (Do et al. 2018). Later, this author described multiple new taxa of marine, terrestrial, and freshwater molluscs from Southeast Asia in a series of papers and books (e.g., Thach 2016a, 2016b, 2017, 2018, 2020a). In summary, these works contain descriptions of one new genus and 12 new nominal species of freshwater Mollusca (Appendix). The new species-group names were attributed to three bivalves and nine gastropods. Several of these species were co-authored/authored by Franz Huber, who is an amateur shell collector from Austria (Thach 2020a). All the Mollusca taxa under discussion conform to the requirements of the International Code of Zoological Nomenclature and must be considered taxonomically available names (see Appendix). The holotypes of these nominal species were deposited in the following museums: North Carolina Museum of Natural Sciences [NCSM], Raleigh, North Carolina, United States of America (8 species); Muséum National d’Histoire Naturelle [MNHN], Paris, France (2 species); British Museum of Natural History [NHMUK], London, United Kingdom (1 species); Royal Belgian Institute of Natural Sciences [IRSNB], Brussels, Belgium (1 species). The protologues contain color images of the type series of each new taxon (Thach 2016b, 2016c, 2018, 2020a). It is nice to see that four names are dedicated to Dr. Arthur Bogan, a prominent American malacologist, who is working in the NCSM (Thach 2016c, 2018, 2020a; see Appendix for detail). These names are as follows: Pseudodon artbogani Thach & Huber in Thach, 2020 and Lanceolaria bogani Thach, 2016 [=L. fruhstorferi (Dautzenberg, 1900)] (Bivalvia: Unionidae), Brotia bogani Thach & Huber in Thach, 2020 (Gastropoda: Pachychilidae), and the genus Boganmargarya Thach, 2018 (Gastropoda: Viviparidae). Although a complete reappraisal of N. N. Thach’s freshwater Mollusca will be published elsewhere, here we would discuss and revise a few remarkable nomenclatural cases which appeared in this work. These examples mostly arose because the author overlooked several historical works on the target taxa. In particular, one genus and five nominal species were described from Lake Inle in Myanmar as follows: Boganmargarya Thach, 2018; Boganmargarya huberi Thach, 2018; Brotia frankhuberi Thach, 2020; B. bogani Thach & Huber in Thach, 2020; Melanoides thachi Huber in Thach, 2020; and Paludomus huberi Thach, 2020 (see Appendix). This lake and surrounding water bodies were a focus of comprehensive surveys, the results of which were published in a special volume of “Records of the Indian Museum” (Vol. 14, 1918) edited by the Director of the Zoological Survey of India Dr. Nelson Annandale. This 214-page volume contains 13 chapters characterizing the geography, geology, natural history, and fauna of this lake in detail (Annandale 1918a). Three chapters comprise the results of taxonomic and morphological research on freshwater malacofauna from the lake (Annandale 1918b, 1918c; Prashad 1918), including the comprehensive “Aquatic Molluscs of the Inle Lake and connected waters” with numerous shell images of gastropods and bivalves (Annandale 1918b). Regrettable, however, N. N. Thach overlooked those historical works, presenting a thorough taxonomic revision of freshwater molluscs from Lake Inle with descriptions of taxa from several families such as Viviparidae, Pachychilidae, Thiaridae, Paludomidae, and others. Hence, a genus and five nominal species described by N. N. Thach from this lake could represent junior synonyms of some already known taxa, and certainly need a revision. The genus Boganmargarya was introduced on the basis of conchological features alone. In the diagnosis, it was compared with Tchangmargarya He, 2013 and Margarya Nevill, 1877 (Thach, 2018). Unfortunately, the author was not aware of the genus Taia Annandale, 1918 that was described from 74 BOLOTOV ET AL. Myanmar. This genus was established for a group of peculiar viviparids from the Salween and Irrawaddy river basins, reaching the maximum species diversity in Lake Inle (Annandale 1918b). In the original description, Annandale (1918b: 124) wrote that “The shells of these remarkable species exhibit affinities both with Vivipara (s.s.) and with Margarya, Nevill; they also have some resemblance to those of Tulotoma, Haldeman”. Furthermore, Annandale (1918b: 124) developed a key for identification of the 11 fossil and recent Taia species from the Shan State of Myanmar based on conchological features. Using this key, we found that the holotype of Boganmargarya huberi undoubtedly belongs to Taia shanensis (Kobelt, 1909). The formal synonymy is proposed here as follows: Taia shanensis (Kobelt, 1909) [=Boganmargarya huberi Thach, 2018 syn. nov.]; and Taia Annandale, 1918 [=Boganmargarya Thach, 2018 syn. nov.] (Gastropoda: Viviparidae). The status of Brotia frankhuberi