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Live snails of the species group I A Rhiostoma haughtoni specimen CUMZ 10048/2 from Dhammathat Cave, Myanmar B–D Rhiostoma samuiense B specimen CUMZ 3989 from Samui Island, Surat Thani C specimen CUMZ 3996 from Perlis, Malaysia (topotype of Rhiostoma chupingense) D specimen CUMZ 4713 of “proboscis” morphotype from Surat Thani E, F copulation pair of Rhiostoma samuiense specimen CUMZ 4713 from Surat Thani shows unsuccessfully transferred spermatophore (female on the right in E and on the left in F) Live snails of the species group II A Rhiostoma housei specimen CUMZ 3987 from Ao Manow, Prachuap Khiri Khan B Rhiostoma hainesi from Khao Soi Dao, Chanthaburi B without breathing device D Rhiostoma jalorensis specimen CUMZ 3994 from Wat Tham Sue, Krabi. in Tongkerd, Tumpeesuwan, Inkhavilay, Prasankok, ... et Sutcharit, 2023. All figures are not to scale. |
Abstract
The snorkel snail genus Rhiostoma Benson, 1860 is comprised of terrestrial cyclophorid snails with wide-ranging species diversity and radiation in Southeast Asia. The typical characters of the genus are a depressed shell, a detached and descending portion of the last whorl with a distinctive peristomal breathing device attached, and a calcareous cup-shaped operculum. Herein, we have revised the systematics of extant species based on shell morphology combined with COI barcoding. From these thirty recognised species, twelve are described as new to science: R. ? amarapuraense sp. nov., R. anceyi sp. nov., R. breviocollar sp. nov., R. ebenozostera sp. nov., R. cheliopegma sp. nov., R. furfurosum sp. nov., R. gnomus, sp. nov., R. lannaense sp. nov., R. laoense sp. nov., R. platymorpha sp. nov., R. rhothonotaphrosa sp. nov., and R. tigrina sp. nov. All conchological characters are provided via illustrations of type specimens and living snails, and descriptions of the shells and radulae. Phylogenetic analysis based on partial COI gene sequences strongly supports the designated morphospecies and a monophyletic Rhiostoma, confirming that all pterocyclinid snails with a calcareous, cup-shaped operculum belong to the same clade. A high intra-specific divergence was observed in R. jalorensis and R. housei populations from locations in close proximity, suggesting a lower dispersal and higher level of isolation. The low inter-specific divergence found in R. hainesi, R. samuiense, R. asiphon, and R. rhothonotaphrosa sp. nov. supports their recent diversification and local adaptation, and is congruent with their marked morphological differences. Finally, nine formerly Rhiostoma-placed species were reclassified into either the genus Cyclotus or the genus Opisthoporus.
Keywords: DNA barcoding, endemic, Indochina, limestones, operculum, Prosobranchia, taxonomy
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| Live snails of the species group I A Rhiostoma haughtoni specimen CUMZ 10048/2 from Dhammathat Cave, Myanmar B–D Rhiostoma samuiense B specimen CUMZ 3989 from Samui Island, Surat Thani C specimen CUMZ 3996 from Perlis, Malaysia (topotype of Rhiostoma chupingense) D specimen CUMZ 4713 of “proboscis” morphotype from Surat Thani E, F copulation pair of Rhiostoma samuiense specimen CUMZ 4713 from Surat Thani shows unsuccessfully transferred spermatophore (female on the right in E and on the left in F), and the red arrows indicate a spermatophore illustrated in Fig. 7D. All figures are not to scale. |
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| Live snails of the species group II A Rhiostoma housei specimen CUMZ 3987 from Ao Manow, Prachuap Khiri Khan B, C Rhiostoma hainesi from Khao Soi Dao, Chanthaburi B without breathing device and C with long breathing device D Rhiostoma jalorensis specimen CUMZ 3994 from Wat Tham Sue, Krabi. All figures are not to scale. Photographs: P. Tongkerd (B, C). |
Piyoros Tongkerd, Sakboworn Tumpeesuwan, Khamla Inkhavilay, Pongpun Prasankok, Ekgachai Jeratthitikul, Somsak Panha and Chirasak Sutcharit. 2023. Systematic Revision of the Snorkel Snail Genus Rhiostoma Benson, 1860 (Gastropoda, Caenogastropoda, Cyclophoridae) with Descriptions of New Species. ZooKeys. 1142: 1-144. DOI: 10.3897/zookeys.1142.90097
