Two new species of terrestrial microsnails of the genus Hypselostoma W.H. Benson, 1856 (Gastropoda, Eupulmonata, Hypselostomatidae) from northeastern Thailand

49 Two new species of terrestrial microsnails of the genus Hypselostoma W.H. Benson, 1856 (Gastropoda, Eupulmonata, Hypselostomatidae) from northeastern Thailand Kitti Tanmuangpak1, Benchawan Nahok2, Utain Chanlabut2, Chanidaporn Tumpeesuwan3, Sakboworn Tumpeesuwan3 1 Program of Biology, Department of Science, Faculty of Science and Technology, Loei Rajabhat University, Mueang District, Loei 42000, Thailand 2 Program of General Science, Faculty of Education and Human Development, Chaiyaphum Rajabhat University, Mueang District, Chaiyaphum 36000, Thailand 3 Department of Biology, Faculty of Science, Mahasarakham University, Kantharawichai District, Maha Sarakham 44150, Thailand Corresponding author: Sakboworn Tumpeesuwan ([email protected]) Copyright: © Kitti Tanmuangpak et al. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract Two new species of hypselostomatid land microsnails, Hypselostoma pongrati Tanmuangpak & S. Tumpeesuwan, sp. nov. from Nong Bua Lamphu Province and H. sichomphuense Tanmuangpak & S. Tumpeesuwan, sp. nov. from Khon Kaen Province, are described based on the morphology of their shell, radula, and genital system. Both new species are very similar in shell shape to H. phupaman from Chaiyaphum Province, possessing a double-keeled last whorl. However, H. pongrati Tanmuangpak & S. Tumpeesuwan, sp. nov. is distinguished by the absence of apertural barriers, whereas H. sichomphuense Tanmuangpak & S. Tumpeesuwan, sp. nov. possesses three apertural barriers, and H. phupaman possesses six or seven. The three species were found on isolated limestone hills in the Chaiyaphum-Khon Kaen-Nong Bua Lamphu-Loei area. Key words: Apertural barriers, double-keeled last whorl, genital system, limestone hills, radula Introduction The land pulmonate microsnails of the genus Hypselostoma W.H. Benson, 1856, were classified into the superfamily Pupilloidea W. Turton, 1831 and family Hypselostomatidae Zilch, 1959 (Gojšina et al. 2025), based on their shell morphology, especially apertural barriers (van Benthem Jutting 1950; Schileyko 1998; Panha and Burch 2008; Sutcharit et al. 2023). This genus has high-spired, conical shells with a free trumpet-shaped last whorl. Panha and Burch (2008) used the separation of the angular and parietal lamellae within the aperture as the key character to distinguish Gyliotrachela Tomlin, 1930 from Hypselostoma. Recently, Gojšina et al. (2025) treated Gyliotrachela and Antroapiculus Panha & J.B. Burch, 2002 as junior synonyms of Hypselostoma, because there are several instances of species from both genera having very similar, if not identical, shell morphologies, while the presence of parietal angular lamellae alone would not justify the separation of the two genera. In their Academic editor: Thierry Backeljau Received: 30 May 2025 Accepted: 20 November 2025 Published: 23 December 2025 ZooBank: https://zoobank. org/2C922940-4004-48BE-A56952F0314F47D2 Citation: Tanmuangpak K, Nahok B, Chanlabut U, Tumpeesuwan C, Tumpeesuwan S (2025) Two new species of terrestrial microsnails of the genus Hypselostoma W.H. Benson, 1856 (Gastropoda, Eupulmonata, Hypselostomatidae) from northeastern Thailand. ZooKeys 1265: 49–67. https://doi.org/10.3897/ zookeys.1265.160661 ZooKeys 1265: 49–67 (2025) DOI: 10.3897/zookeys.1265.160661 50 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand taxonomic revision, Gojšina et al. (2025) concluded that the updated number of species of Hypselostoma is now 95 species (85 verified species + 10 unverified species from the Philippines), and that this genus is widely distributed in Southeast Asia and north and west Australia, Japan, and China (van Benthem Jutting 1950, 1962; Solem 1981; Schileyko 1998; Panha et al. 2004; Panha and Burch 2008; Tongkerd et al. 2013; Gojšina et al. 2025) (Table 1, Fig. 1). The two new species of Hypselostoma described in this paper were recently discovered on a wall in limestone hills covered with mixed-deciduous forest in Nong Bua Lamphu and Khon Kaen Provinces, northeastern Thailand. Figure 1. Map of Southeast Asia and the surrounding area showing the type localities of the known Hypselostoma spp. The numbers correspond to the species numbers listed in Table 1. 51 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand Table 1. Nominal species and subspecies of Hypselostoma and their reported distribution (excluding the uncertain records from the Philippines). S/N Species name Localities References 1H. tubiferum (W.H. Benson, 1856) Thyet-Mio, Irawadi Burmanici, Myanmar 3 2H. bensonianum W.T. Blanford, 1863 Mandalay Division, Myanmar 1, 3, 4, 18 3H. crossei Morlet, 1886 Lang-son, Tonkin, Vietnam; Tianxingqiao Town, Zhenning Bouyeizu Miaozu Zizhixian, Guizhou, China; Nawit Village, Viengxay District, Houaphane, Laos 3, 6, 25 4H. hungerfordianum Möllendorff, 1891 Bukit Baling, Kedah; Gunong Pondok, Perak; Batu Caves, Selangor; Bukit Chintamani and Gua Bama, Pahang, Malaysia; Kuankalong Limestone Hill, Satun; Samui Islands, Thailand 3, 7, 8, 29 5H. transitans Möllendorff, 1894 Samui Islands, Surat Thani and Chumphon, Thailand 3, 25, 26, 33 6H. everetti E.A. Smith, 1896 Timor Island, Kalao Island, Sulawesi, Java, Bali, Lesser Sunda Islands and Tanimbar Islands, Indonesia 3, 21, 33 7H. fruhstorferi Möllendorff, 1897 West Java Province, Djampang, Java, and Makalé to Kalossi, Sulawesi, South Celebes, Indonesia 3, 30 8H. annamiticum Möllendorff, 1900 Phuc-Son, Touranne, Annam, Vietnam 3 9H. kelantanense (Sykes, 1902) Kelantan and Kota Tongkat, Pahang, and Kramat Pulai, Perak, Malaysia 3 10 H. insularum Pilsbry, 1908 Yonakunijima, Ryuyku, Japan; Kenting Tropical Botanical Garden, Hengchun, Pingtung, Taiwan 3 11 H. australe australe Odhner, 1917 Chillagoe Caves, Queensland, Australia 3, 22 12 H. terae Tomlin, 1939 Bukit Chintamani, Pahang, and Bukit Charas, Pahang, and Bukit Takun, Kanching, Selangor, Malaysia 3 13 H. depressispira (van Benthem Jutting, 1949) Bukit Chintamani; Gua Bama, Pahang, Bukit Panching, Pahang Malaysia 3, 7, 29 14 H. piconis van Benthem Jutting, 1949 Sungei Siput, Perak, Malaysia 3 15 H. elephas van Benthem Jutting, 1950 Bukit Tenggek, Pahang, Malaysia 3 16 H. emergens (van Benthem Jutting, 1950) Bukit Chuping, Perlis, Malaysia 3, 7, 28 17 H. frequens (van Benthem Jutting, 1950) Kota Tongkat, Pahang and Gunong Batu Kurau, Perak, Malaysia 3 18 H. luctans (van Benthem Jutting, 1950) Gunong Pondok, Padang Rengas, Perak, Malaysia 3, 7, 32 19 H. modestum (van Benthem Jutting, 1950) Gua Musang, Kelantan and Peninsular Siam, Malaysia 3, 7, 32 20 H. serpa (van Benthem Jutting, 1950) Baling, Kedah, Malaysia; Tarutoa National Park, Satun and Krabi, Thailand 3 21 H. troglodytes (van Benthem Jutting, 1950) Gua Bama, Padang Tengku, Pahang, Malaysia 3, 7, 28 22 H. venustum (van Benthem Jutting, 1950) Gunong Pondok, Padang Rengas, Perak, and Kota Tongkat, Pahang, Malaysia 3 23 H. saxicola (van Benthem Jutting, 1960) Kampong Tebing Tinggi, Kangar, Perlis, Malaysia 3, 31 24 H. salpinx (van Benthem Jutting, 1961) Bukit Serdam, Pahang, Malaysia 3 25 H. cambodjense van Benthem Jutting, 1962 Kampot, Cambodia; Kien Giang, Vietnam 3 26 H. dilatatum van Benthem Jutting, 1962 Binh An Commune, Ba Nui Village, Mo So Cave, Kien Luong District Kien Giang, Vietnam 3 27 H. rupestre van Benthem Jutting, 1962 Kien Giang, Vietnam; Kampot, Cambodia 3 28 H. torticollis (van Benthem Jutting, 1962) Phum Troung Mean, Banan District, Battambang, Cambodia 3, 23 29 H. australe napieranum (Solem, 1981) Yammera Gap and Napier Range, Kimberley Region, Western Australia, Australia 3, 22 30 H. paini (F.G. Thompson & Dance, 1983) Deer Cave, Melinau Paku Valley, Fourth Division, Sarawak, Borneo, Malaysia 3 31 H. procerum (F.G. Thompson & Dance, 1983) Gunong Budah, Medalam Valley, Fifth Division, Sarawak, Borneo, Malaysia 3 32 H. holimanae F.G. Thompson & H.G. Lee, 1988 Kanchanaburi Agricultural College, Mueang District, Kanchanaburi, Thailand 3 33 H. adela (F.G. Thompson & Upatham, 1997) Ban Na San District, Surat Thani, Thailand 17, 25 34 H. burchi (Panha, 1998) Phatthalung, Surat Thani, and Phetchaburi, Thailand 3, 11, 17 35 H. chedi Panha, 1998 Tebpratan Nature Reserve area, Kamphaeng Phet, Thailand 3 36 H. cucumense Panha, 1998 Kangkrajan National Park, Phetchaburi, Thailand 3 37 H. khaowongense Panha, 1998 Takli District, Nakhon Sawan; Tepitak Tamaram Temple, Tepitak Mountain, Mueang Saraburi District, Saraburi; Muangon Cave, San Kam Pang District, Chiang Mai, Thailand 3, 13, 17 38 H. edentatum (Panha & J.B. Burch, 2002) Tamphatai National Park, Ngao District, Lampang; Ban Pa Ngae Limestone Knoll, Padaet District, Chiang Rai, Thailand 3 39 H. khaochongpran (Panha & J.B. Burch, 2002) Khaochongpran, Tao Pun Sub-District, Photharam District, Ratchaburi, Thailand 3 40 H. muaklekense (Panha & J.B. Burch, 2002) Tepitak Mountain, Muaklek District, Saraburi, Thailand 3, 15, 17 41 H. pendulum (Panha & J.B. Burch, 2002) Chonglom Mountain, Bhumiphol Dam Reservoir, Samngao District, Tak, Thailand 3 42 H. phupaman (Panha & J.B. Burch, 2002) Phuphaman Mountain, Phetchabun, Thailand 3 43 H. sichang (Panha & J.B. Burch, 2002) Sichang Island, Si Racha District, Chonburi, Thailand 3, 14, 17 52 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand S/N Species name Localities References 44 H. chatnareeae (Panha & J.B. Burch, 2003) Tam Sua Temple, Utong District, Suphanburi, Thailand 3 45 H. diarmaidi (Panha & J.B. Burch, 2003) Pluangthong Mountain, Botong District, Chonburi, Thailand 2, 3, 17 46 H. erawan Panha & J.B. Burch, 2003 Erawan National Park, Sai Yok District, Kanchanaburi, Thailand 3 47 H. panhai J.B. Burch & Tongkerd, 2003 Chongkhaokad, Sai Yok District, Kanchanaburi, Thailand 3 48 H. khaochakan (Panha & J.B. Burch, 2003) Chakan Mountain, Khaochakan Temple, Khaochakan District, Sa Kaeo, Thailand 2, 3, 17 49 H. kohrin (Panha & J.B. Burch, 2003) Kohrin (Rin Island), Chonburi, Thailand 2, 3, 17 50 H. surakiti (Panha & J.B. Burch, 2003) Puttabanpot Temple, Nawang District, Nong Bua Lamphu, Thailand 2, 3, 17 51 H. taehwani Panha & J.B. Burch, 2003 Central Area of Tamrong Temple, Mueang Phetchaburi District, Phetchaburi, Thailand 3 52 H. khaowongkot (Panha & J.B. Burch, 2004) Khaowongkot, Ban Mi District, Lopburi, Thailand 3, 16, 17 53 H. pattalungense Panha & J.B. Burch, 2004 Limestone Hill in Ko Si Ko Ha (Ko Na Thewada), Phatthalung, Thailand 3 54 H. smokon (Panha & J.B. Burch, 2004) Smokon Mountain, Ban Mi District, Lopburi, Thailand 3 55 H. srakeoense (Panha & J.B. Burch, 2004) Plubpluengtong Limestone Hills, Sa Kaeo, Thailand 3, 23 56 H. tridentatum (Panha & J.B. Burch, 2004) Plubpluengtong Limestone Hills, Sa Kaeo, Thailand 3, 16, 17 57 H. utongensis Panha & J.B. Burch, 2004 Tam Sua Hill, Utong District, Suphanburi, Thailand 3 58 H. loei Panha & Prateespasen, 2006 Limestone Hills in Loei, Phitsanulok, Khon Kaen and Nong Bua Lamphu, Thailand 3 59 H. benetuitum Vermeulen, Luu, Theary & Anker, 2019 Phnom Kampong Trach, Kampot, Cambodia 3 60 H. chaunosalpinx (Vermeulen, Luu, Theary & Anker, 2019) Kampong Trach Area, Phnom Kampong Trach, Kampot, Cambodia 3 61 H. depressum (Vermeulen, Luu, Theary & Anker, 2019) Phnom La’Ang Cave, Kampot Area, Kampot, Cambodia 3 62 H. discobasis Vermeulen, Luu, Theary & Anker, 2019 Phnom La’Ang, Kampot Area, Kampot, Cambodia 3 63 H. cultura (Tanmuangpak & Dumrongrojwattana, 2022) Agricultural Areas in Mueang Loei District, Loei; Lampang and Chonburi, Thailand 3, 24 64 H. khmerianum (Sutcharit & Panha, 2023) Phnom Sampeov Mountain, Banan District, Battambang, Cambodia 3, 23 65 H. aunglini (Tongkerd & Panha, 2024) Kaw Gon Cave, Hpa-An, Kayin State, Myanmar 3, 27 66 H. aenigma Gojšina, Grego & Páll-Gergely, 2025 Pan Do Mi Mountain, Phon Tho Village, Kamarmaung, Kayin State, Myanmar 3 67 H. aquila Gojšina, Hunyadi & Páll-Gergely, 2025 Chap Phleung Mountain, Stung Treng Mekong Bridge, Steung Treng, Cambodia 3 68 H. bubalus Gojšina, Hunyadi & Páll-Gergely, 2025 Kodiang, Gua Kerbau, Kedah, Malaysia 3 69 H. circumcarinatum Gojšina, Auffenberg & Páll-Gergely, 2025 Taoist Buddhist Temple, Kanchanaburi, Thailand 3 70 H. coriaceum Gojšina & Páll-Gergely, 2025 Tanjung Rhu Beach, Langkawi Island, Malaysia 3 71 H. fortunatum Gojšina, Hunyadi & Páll-Gergely,2025 Khao Ok Thalu, Phattalung; & Songkhla, Thailand 3 72 H. fungus Gojšina, Hunyadi & Páll-Gergely, 2025 Stung Treng Mekong Bridge, Phnom Chhnok, Stung Treng , Cambodia 3 73 H. geckophilum Gojšina, Hunyadi & Páll-Gergely, 2025 Tham Khao Wongkot, Kaeng Hang Maeo District, Chanthaburi, Thailand 3 74 H. iunior Gojšina & Páll-Gergely, 2025 Ban Pha Tun, Tham Pha Tup Forest Park, Mueang Nan District, Nan, Thailand 3 75 H. ophis Gojšina, Hunyadi & Páll-Gergely, 2025 Khao Ok Thalu, Phatthalung, Thailand 3 76 H. platybasis Gojšina, Hunyadi & Páll-Gergely, 2025 Stung Treng Mekong Bridge, Chap Phleung Mountain, Steung Treng, Cambodia 3 77 H. populare Gojšina, Hunyadi & Páll-Gergely, 2025 Krabi, Chumphon and Ranong, Thailand 3 78 H. sculpturatum Gojšina, Hunyadi & Páll-Gergely, 2025 Stung Treng Mekong Bridge, Phnom Chhnok, Steung Treng, Cambodia 3 79 H. similare Gojšina, Hunyadi & Páll-Gergely, 2025 Wat Tham Khao Prathun, Khao Chamao District, Rayong, Thailand 3 80 H. sorormajor Gojšina, Hunyadi & Páll-Gergely, 2025 Stung Treng Mekong Bridge, Chap Phleung Mountain, Steung Treng, Cambodia 3 81 H. sororminor Gojšina, Hunyadi & Páll-Gergely, 2025 Stung Treng Mekong Bridge, Chap Phleung Mountain, Steung Treng, Cambodia 3 82 H. tertiusfrater Gojšina & Páll-Gergely, 2025 Gunong Subis; Sarawak & Sabah in Borneo, Malaysia 3 83 H. torta Gojšina, Auffenberg & Páll-Gergely, 2025 Nakhon Sawan, Thailand 3 84 H. vesovici Gojšina & Páll-Gergely, 2025 Gua Telinga, Kuala Tahan, Taman Negara, Jerantut, Pahang, Malaysia 3 85 H. vicinum Gojšina, Auffenberg & Páll-Gergely, 2025 Surat Thani, Thailand 3 86 H. vujici Gojšina & Páll-Gergely, 2025 Ban Non San Village, Nakhon Sawan, Thailand 3 87 H. pongrati sp. nov. Si Bun Rueang District, Nong Bua Lamphu, Thailand This study 88 H. sichomphuense sp. nov. Si Chomphu District, Khon Kaen, Thailand This study References: 1 = Blanford (1863); 2 = Burch et al. (2003); 3 = Gojšina et al. (2025); 4 = Gude (1914); 5 = Inkhavilay et al. (2016); 6 = Inkhavilay et al. (2019); 7 = Maassen (2001); 8 = Möllendorff (1891); 11 = Panha (1998a); 12 = Panha (1998b); 13 = Panha (1998c); 14 = Panha and Burch (2002a); 15 = Panha and Burch (2002b); 16 = Panha et al. (2004); 17 = Panha and Burch (2008); 18 = Pilsbry (1917a); 19 = Pilsbry (1917b); 21 = Smith (1896); 22 = Solem (1981); 23 = Sutcharit et al. (2023); 24 = Tanmuangpak and Dumrongrojwattana (2022); 25 = Thompson and Upatham (1997); 26 = Tongkerd et al. (2013); 27 = Tongkerd et al. (2024); 28 = van Benthem Jutting (1949); 29 = van Benthem Jutting (1950); 30 = van Benthem Jutting (1952); 31 = van Benthem Jutting (1960); 32 = van Benthem Jutting (1962); 33 = Vermeulen and Whitten (1998); 34 = Vermeulen et al. (2019). 53 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand The external shell morphology of the two new species is very similar to that of Hypselostoma phupaman (Panha & J.B. Burch, 2002c) from Chaiyaphum Province (Panha and Burch 2008), with which they share the double-keeled last whorl, but from which they differ by their number of apertural barriers. These three species are also similar to Hypselostoma torta Gojšina, Auffenberg & Páll-Gergely, 2025 from Nakhon Sawan Province (Gojšina et al. 2025) with which they share their shell shape, as well as the strongly shouldered penultimate and last whorls. However, H. torta differs as it has only one keel on the last whorl, instead of two. Materials and methods Microsnail specimens were collected during November–December 2021 and January 2022 from limestone hill in Nong Bua Lampu Province (Figs 1, 2A, B), and Khon Kaen Province (Figs 1, 2C, D), northeastern Thailand. Complete adult shells were used to count the number of whorls and measure shell height (SH), shell width (SW), aperture height (AH), and aperture width (AW) with digital vernier calipers (Electronic Digital Calliper S.H.). Shells and radulae were photographed by a scanning electron microscope (LEO 1450 VP) at the Microscope Center, Faculty of Science, Burapha University and Centre for Scientific and Technological Equipment at Suranaree University of Technology. Adult microsnails were dissected under a stereomicroscope to examine their genital system and extract their radula from the buccal mass. The radula sac was soaked in 5% NaOH solution to separate and clear the radula. Species identification was based on Pilsbry (1916–1918), van Benthem Jutting (1950), Panha and Burch (2008), and Gojšina et al. (2025). Shell characters were examined following Panha and Burch (2008) and Gojšina et al. (2025), whereas characters of genitalia and radula were studied following Dumrongrojwattana and Tanmuangpak (2020) and Tanmuangpak and Dumrongrojwattana (2022). The type material was deposited in the following institutions: NHLRU Natural History Museum of Loei Rajabhat University (Loei, Thailand) and NHMSU Natural History Museum, Mahasarakham University (Maha Sarakham, Thailand). Results Taxonomy Family Hypselostomatidae Zilch, 1959 Genus Hypselostoma W.H. Benson, 1856 Diagnosis. Shell tiny, turbinate, high-spired, or discoidal. Peristome adnate or separated from the adjacent body whorl forming a tuba; edge of peristome expanded. Aperture with four or more parietal and angular apertural lamellae or plicae (barriers), except in Hypselostoma edentatum (Panha & J.B. Burch, 2002d) and H. pongrati sp. nov. which have no apertural barriers and H. sichomphuense sp. nov. which has only three barriers (Panha and Burch 2008; Gojšina et al. 2025). The genitalia of Hypselostoma possess a penis that is more swollen than the epiphallus; gametolytic sac connects to vagina very close to atrium, divided into two 54 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand parts, with the proximal part swollen and larger than the penis (except in H. cultura (Tanmuangpak & Dumrongrojwattana, 2022), in which the gametolytic sac has a long duct between proximal and distal part, while there is no swollen proximal part in H. depressispira (Berry, 1963)). These anatomical characters differ from the genus Aulacospira Möllendorff, 1890, whose gametolytic sac connects to the vagina far from the atrium (Dumrongrojwattana and Tanmuangpak 2020) Hypselostoma pongrati Tanmuangpak & S. Tumpeesuwan, sp. nov. https://zoobank.org/C545C51C-2464-468F-983B-9713B28FEFBC Figs 2A, B, 3A–I, 5A–E, 6A, B; Table 2 Hypselostoma sp. – Tanmuangpak & Kaewsawang, 2025: 20, 23, 25, 27, 29–31, fig. 2q. Material examined. Holotype: Thailand • 1 empty shell; Nong Bua Lamphu Province, Sri Bun Rueang District, Pha Sam Yod limestone hill (17°10'02.020"N, 102°02'03.020"E) covered by mixed-deciduous forest; 20.xi.2021, leg. Tanmuangpak, K. (NHLRU014) (Fig. 3A–E). Paratypes: Thailand • 12 specimens Figure 2. Living Hypselostoma spp. A, B. Hypselostoma pongrati sp. nov. paratype NHLRU015; C, D. Hypselostoma sichomphuense sp. nov. paratype NHLRU033. 55 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand preserved in 70% ethanol (NHLRU015–026); • five shells (NHLRU027–031); • three specimens preserved in 70% ethanol (NHMSU–00063–B); • two shells (NHMSU–00063). All paratypes collected from the same location as holotype, leg. Tanmuangpak, K. 10.xii.2021. Measurements. Holotype: SH = 4.48 mm, SW = 3.34 mm, AH = 1.95 mm, AW = 1.92 mm. Paratypes (19 specimens measured): SH = 4.48–6.02 mm (5.58 ± 0.42 mm), SW = 3.07–4.12 mm (3.72 ± 0.36 mm), AH = 1.95–2.64 mm (2.24 ± 0.20 mm), AW = 1.68–2.42 mm (1.99 ± 0.16 mm) (Fig. 7). Diagnosis. This new species has a prominent keel on the upper part of the last whorl and a weaker keel on the lower part. Apertural barriers absent (Fig. 3A, G, H, L). Terminal part of the last whorl is adnated to penultimate whorl. Description. Shell (Fig. 3A–I) concave-conical, high spired, with 4¾ whorls. Large size for the genus, with shell height 4.48–6.02 mm, shell width 3.07– 4.12 mm. The suture is deep. Protoconch smooth, with 1–1½ whorls that gradually increase in size to the teleoconch whorls. Teleoconch with 3–3¾ whorls, Figure 3. Shell morphology of Hypselostoma pongrati sp. nov. holotype NHLRU014. A. Apertural view; B. Lateral view; C, E, F. Protoconch view; D. Umbilical view apertural detail; G–I. Apertural view in different angles. 56 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand very fine spiral striation the body whorl widest, possesses two keels (upper one more prominent than the lower one). Apertural barriers absent. Peristome thickened and expanded. The parietal and convex angulo-palatal embayments form a sinulus, thickened, and expanded. The basal peristome is smooth and expanded, columellar side is more expand than the angulo-palatal side. Genital system (Fig. 6A, B). Atrium shorter than the vagina. Penis shorter than the epiphallus, its anterior portion is a short and bulged tube, and the distal end of the penis bulge. Epiphallus connects to the distal end of the penis, shorter than vas deferens, anterior portion slender and cylindrical, its central portion more slender than the anterior portion, posterior portion curved, white glossy. Penial retractor muscle absent. Vas deferens long, slender, entering the epiphallus apically. The vagina and free oviduct are cylindrical, and the vagina is shorter than the free oviduct. The gametolytic sac is a long tube, with a swollen proximal part, and larger than penis, surrounded by a thin sheath and connected to the proximal part of the vagina, whose distal end is long, slender, and curved. Uterus large, with very thin prostate gland attached to it. Hermaphroditic duct loosely convoluted. The albumen gland large and yellowish. Dart apparatus absent. Radula (n = 4) (Fig. 5A–E). Radula comprises 173–184 (179 ± 4.93) transverse rows of teeth each row containing 25–27 teeth. Radula formula (7-8)+5+1+5+(78). Central tooth small, unicuspid, elongated triangular. Lateral teeth bicuspid and asymmetrical, consisting of a large lanceolate endocone and smaller elongated triangular ectocone. Five lateral teeth on each side of the central tooth, the first tooth largest, and gradually smaller outwards. Marginal teeth start at 6th tooth outwards from central teeth, which almost changed to tricuspids. On each outer side of the lateral teeth there are seven or eight marginal teeth. Etymology. This new species is dedicated to the late Pongrat Dumrongrojwattana, our highly respected senior who was an expert on microsnails and who provided us with many land snails references, knowledge, and inspiration. Table 2. Comparison of shell, radula, and genital system of Hypselostoma pongrati sp. nov., H. sichomphuense sp. nov., H. cultura and Aulacospira vanwalleghemi. Characters Species H. pongrati sp. nov. H. sichomphuense sp. nov. H. cultura A. vanwalleghemi Shell: Shape Conical Concave-conical Concave-conical Conical-ovoid Shell height (mm) 4.48–6.02 3.82–4.29 2.11–2.25 1.87–3.17 Shell width (mm) 3.07–4.12 3.12–4.12 2.50–2.80 1.74–3.28 Appearance of the last whorls double keeled double keeled keeled at the center of the periphery keeled above the center of the periphery Apertural barrier absent 3 26 absent Radula Formula (7-8):5:1:5:(7-8) (9-10):7:1:7:(9-10) 8:5:1:5:8 (7-8):4:1:4:(7-8) Genital system: Penial retractor muscle (pr) absent short tube Bulged and curved Short and rounded Gametolytic sac anterior portion bulge, larger than penis anterior portion bulge, equal to penis anterior portion bulge smaller than penis anterior portion bulge, smaller than penis distal end long cylindrical and curved. distal end long cylindrical and curved distal end bulged posterior portion long slender, curved References This study This study Tanmuangpak and Dumrongrojwattana (2022) Dumrongrojwattana and Tanmuangpak (2020) 57 ZooKeys 1265: 49–67 (2025), DOI: 10.3897/zookeys.1265.160661 Kitti Tanmuangpak et al.: Two new species of Hypselostoma from northeastern Thailand Animal and ecology. Living animals have a cream-colored body and foot, while their head and tentacles are rather black, with black eyes located at the tip of the ocular tentacle. This species was found on the limestone wall in the mixed-deciduous forest (Fig. 2A, B). Distribution. This species was found only on limestone wall in Pha Sam Yod, Si Bun Rueang District, Nong Bua Lamphu Province. Remarks. Hypselostoma pongrati sp. nov. from Si Bun Rueng District, Nong Bua Lam Phu Province, is quite different in shell shape from almost all other Hypselostoma species in Thailand. It is similar in shell shape to the geographically close H. phupaman from Chaiyaphum Province and H. sichomphuense sp. nov. from Si Chomphu, Khon Kaen Province. The unique characteristics of H. pongrati sp. nov. are the lack of apertural barriers and the last whorl adnate to the penultimate whorl, peristome thick, expanded and not reflected. It is strongly expanded at the parietal side where it leans against penultimate whorl and forms a thick crescent callus. Three species possess a double-keeled last whorl, but the lower keel is weak in both H. pongrati sp. nov. and H. sichomphuense sp. nov. Other similar species are H. torta from Nakhon Sawan Province, Thailand and H. platybasis from Steung Treng Province, Cambodia (Gojšina et al. 2025). In H. torta and H. pongrati sp. nov. all teleoconch whorls are shouldered, but in H. torta the last whorl is detached from the penultimate whorl. There are four weak apertural barriers. The columellar barriers form as a rather strong swelled part of the aperture which forms a prominent basal furrow below it. Hypselostoma platybasis differs from H. pongrati sp. nov. by possesses bluntly keeled penultimate at the center of the periphery and shouldered last whorl. Last whorl very slightly detached from the penultimate whorl and with a sharp shoulder. Apertural barriers few and relatively weak. In H. pongrati sp. nov. there is no penial retractor muscle, and the free oviduct is longer than the anterior portion of the gametolytic sac. Conversely, in H. sichomphuense sp. nov. there is a penial retractor muscle, and the free oviduct is shorter than the anterior portion of the gametolytic sac. Hypselostoma sichomphuense Tanmuangpak & S. Tumpeesuwan, sp. nov. https://zoobank.org/EAE8D792-E347-4F2C-9BDB-2291A398D89C Figs 2C, D, 4A–I, 5F–L, 6C, D; Table 2 Material examined. Holotype: Thailand • 1 empty shell Khon Kaen Province, Si Chomphu District, limestone wall in mixed-deciduous forest, Phu Pha Kham (16°50'22.001"N, 102°03'59.001"E), 21.xi.2021, leg. Tanmuangpak, K. (NHLRU032) (Fig. 3G–K). Paratypes: Thailand • 12 specimens preserved in 70% ethanol (NHLRU033–044) (Fig. 2C, D); • two shells (NHLRU045–046); • four specimens preserved in 70% ethanol (NHMSU–00064-B); • one shell (NHMSU–00064). 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