Ecologica Montenegrina, 41, 2021, 73-83 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. BOLOTOV 1,2 , EKATERINA S. KONOPLEVA 1,2, *, ILYA V. VIKHREV 1,2 , MIKHAIL Y. GOFAROV 1,2 , MANUEL LOPES-LIMA 3,4,5 , ARTHUR E. BOGAN 6 , ZAU LUNN 7 , NYEIN CHAN 7 , THAN WIN 8 , OLGA V. AKSENOVA 1,2 , ALENA A. TOMILOVA 1 , KITTI TANMUANGPAK 9 , SAKBOWORN TUMPEESUWAN 10 & ALEXANDER V. KONDAKOV 1,2 1 N. Laverov Federal Center for Integrated Arctic Research of the Ural Branch of the Russian Academy of Sciences, Northern Dvina Emb. 23, 163000 Arkhangelsk, Russia. 2 Northern Arctic Federal University, Northern Dvina Emb. 17, 163002 Arkhangelsk, Russia. 3 CIBIO/InBIO – Research Center in Biodiversity and Genetic Resources, University of Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas 7, 4485-661 Vairão, Portugal. 4 CIIMAR/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. 5 SSC/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. 6 North Carolina Museum of Natural Sciences, 11 West Jones St., Raleigh, NC 27601, United States of America 7 Fauna & Flora International – Myanmar Programme, Yangon, Myanmar. 8 Department of Zoology, Dawei University, Dawei, Tanintharyi Region, Myanmar. 9 Department of Science, Faculty of Science and Technology, Loei Rajabhat University, Loei, Thailand. 10 Department of Biology, Faculty of Science, Mahasarakham University, Maha Sarakham, Thailand. *Corresponding author: es.konopleva@gmail.com 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: 73-83 (2021) This journal is available online at: www.biotaxa.org/em http://dx.doi.org/10.37828/em.2021.41.11