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| Georissa principalis Buathanom & Tongkerd, Georissa chatra Buathanom & Pholyotha, in Buathanom, Tongkerd, Jirapatrasilp, Janjai, Mitchueachart, Annate, Panha, Sutcharit et Pholyotha, 2025. |
Abstract
This paper introduces two newly discovered endemic micro snails, Georissa chatra Buathanom & Pholyotha, sp. nov. and G. principalis Buathanom & Tongkerd, sp. nov., from limestone hills of Uthai Thani and Nakhon Sawan Provinces in central Thailand. These findings expand the number of Georissa species recorded in Thailand to seven. The taxonomic status and species boundaries of these new species were determined through a comprehensive analysis of comparative morphology and mitochondrial genetics. Georissa chatra sp. nov. is distinguished by a conical shell with tall and prominent carinas. Georissa principalis sp. nov. is characterized by an elongate conical or turreted shell with prominent cord-like spiral ridges, and an operculum with two layers. The cytochrome c oxidase subunit I (COI) phylogeny supports the monophyly of both lineages, but the relationships with other congeners remain unresolved. The analysis also revealed interspecific genetic distances among examined species ranging from 6.8% to 18.6%. Additionally, intraspecific genetic distances are surprisingly high, with 6.1% for G. chatra sp. nov. and 7.5% for G. principalis sp. nov. The observed high intraspecific genetic divergences are likely due to the significant endemism and fragmented distribution of populations within karst ecosystems. As a result, the discovery of these two new species significantly advances our understanding of micro snail diversity and represents a crucial first step in establishing a comprehensive DNA barcode reference library for micro snails in Thailand.
Keywords: COI, Endemic, Limestone, Operculated snail, Morphology, Systematics, Taxonomy, Hydrocenoidea
Subclass Neritimorpha Koken, 1896
Order Cycloneritida Frýda, 1998
Superfamily Hydrocenoidea Troschel, 1857
Family Hydrocenidae Troschel, 1857
Genus Georissa Blanford, 1864
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| Living Georissa chatra sp. nov. from a limestone hill near Wat Si Uthum Phon, Nakhon Sawan. A, B.snails in microhabitats on the limestone wall; insets showing close-up views of (A) a snail hiding in a small crevice and (B) a snail on a bare wall. C–F.four different individuals while climbing slowly on moist tissue paper. |
Georissa chatra Buathanom & Pholyotha, sp. nov.
Diagnosis.− Shell minute, conical, dark orange, with tall and prominent carinas: one on upper periphery and one on below periphery.
Etymology.− The specific epithet “chatra” refers to a dome or umbrella-like structure sometimes with multiple tiers or layers, which is used in several Asian royal or state ceremonies, reflecting the distinctive shell shape of this new species.
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| Shells of Georissa principalis sp. nov. A–C.paratype CUMZ 15273 from Wat Khao Mano, Nakhon Sawan. |
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| Living Georissa principalis sp. nov. A.snail in a microhabitat on the limestone wall at Tham Khao Kaji, Uthai Thani; an inset showing a close-up view of a snail among lichen on a bare wall. B–E.four different individuals while climbing slowly on moist tissue paper, (B, C)from Wat Khao Ruea, Nakhon Sawan and (D, E)from Wat Khao Mano, Nakhon Sawan. |
Georissa principalis Buathanom & Tongkerd, sp. nov.
Diagnosis.− Shell minute, elongate, turreted, yellow-orange to light brownish, with about six to seven prominentspiral ridges at the periphery, and operculum with 2 layers.
Etymology.− The name “principalis” is derived from the Latin word meaning “chief” or “leader” and is chosen to honor Her Royal Highness Princess Maha Chakri Sirindhorn for her outstanding leadership in biodiversity conservation in Thailand.
Paniwat BUATHANOM, Piyoros Tongkerd, Parin Jirapatrasilp, Teerangkul Janjai, Bowornluk Mitchueachart, Supunya Annate, Somsak Panha, Chirasak Sutcharit and Arthit Pholyotha. 2025. Phylogenetic and Morphological Evidence for Two New Species of Terrestrial Micro Snail Genus Georissa Blanford, 1864 (Neritimorpha: Hydrocenidae) from Central Thailand. Tropical Natural History. Supplement 8 (2025): 62-78. DOI: 10.58837/tnh.25.8.267040
