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Angustopila coprologos Páll-Gergely, Jochum & Hunyadi; Angustopila psammion Páll-Gergely, Vermeulen & Anker; Angustopila pallgergelyi, Acmella nana, Notharinia micro in Páll-Gergely, Jochum, Vermeulen, Anker, Hunyadi, et al., 2022. |
Abstract
Two new, extremely small land snail species, Angustopila coprologos Páll-Gergely, Jochum & Hunyadi n. sp. and Angustopila psammion Páll-Gergely, Vermeulen & Anker n. sp. are described from northern Vietnam and northern Laos, respectively. The former is characterized by a rough surface sculpture and bears tiny mud granules arranged in a pattern of radial lines on its shell surface. The latter species is the new global record-holder of the tiniest land snail title, with a shell width of 0.6–0.68 mm and a shell height of 0.46–0.57 mm. These measurements surpass the former records of Angustopila pallgergelyi and Acmella nana.
Keywords: Acmella; Angustopila; Arinia; miniaturization; shell; ornamentation
Systematic descriptions
Family Hypselostomatidae Zilch, 1959
Genus Angustopila Jochum, Slapnik & Páll-Gergely, 2014
Angustopila Jochum, Slapnik & Páll-Gergely, 2014; Jochum et al., 2014: 410: 26.
Type species: Systenostoma tamlod Panha & Burch, 1999, by original designation.
Angustopila coprologos Páll-Gergely, Jochum & Hunyadi n. sp.
Diagnosis: A strongly depressed-globular Angustopila species with a wide umbilicus, strong spiral sculpture consisting of a series of coarse elevations (flat-topped beads) in a chain-like pattern and four well-developed teeth (1 parietal, 2 palatal, 1 basal).
Differential diagnosis: Angustopila coprologos n. sp. can be easily distinguished from all other Angustopila species by its depressed shell, the four apertural denticles and the pronounced sculpture.
Etymology: The specific epithet coprologos (Ancient Greek for dung gatherer) refers to the mud granules (here assumed to be faeces) placed on this species’ shell. Used as a noun in apposition.
Distribution: This species is known only from the type locality in Bolikhamsay Province, Laos: ca. 13 km southeast (in a straight line) from the town Lak Sao (see also supplementary figs S1–S2).
Angustopila psammion Páll-Gergely, Anker & Vermeulen, n. sp.
Diagnosis: An Angustopila species with a depressed-globular shell with dome-shaped spire, thick spiral striae, kidney-shaped aperture with single parietal denticle not reaching parietal callus.
Differential diagnosis: Angustopila pallgergelyi Dumrongrojwattana, Chuenit & Wongkamhaeng, 2021 is similar in shell and aperture shape, but is larger, has a prominent palatal tooth (absent in Angustopila psammion n. sp.) and a stronger parietal tooth. Angustopila coprologos n. sp. is slightly larger, has a rough shell surface, and has an additional subcolumellar tooth and two palatal teeth.
Etymology: The specific epithet (ψαμμίον) means a grain of sand in Greek and is used as a noun in apposition.
Distribution: This new species is known only from the type locality, Cap La Cave, Ha Long Bay, Quang Ninh Province, Vietnam.
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| Size comparisons of the former record holders, Angustopila pallgergelyi, Acmella nana, Notharinia micro, the smallest marine snail, Ammonicera minortalis, and the two new species [Angustopila coprologos n. sp. and Angustopila psammion n. sp.] described herein. The image of Ammonicera minortalis Rolán, 1992 is from Oliver et al. (2012), whereas the other images (Acmella nana and Arinia micro) are from their respective original descriptions. The figure of Acmella nana is adjusted to scale with the measurement of the smallest specimen, whereas for Angustopila coprologos n. sp. and Angustopila psammion n. sp., the holotypes (not the tiniest shells) are shown. |
Conclusions:
Two species, Angustopila psammion Páll-Gergely, Vermeulen & Anker n. sp. and Angustopila coprologos Páll-Gergely, Jochum & Hunyadi n. sp. are described from northern Laos and northern Vietnam, respectively. With its shell width of 0.60–0.68 mm and shell height of 0.46–0.57 mm, Angustopila psammion n. sp. is the new global record-holder of the title of the tiniest land snail, surpassing the former two record-holders, Angustopila pallgergelyi and Acmella nana. The calculated volume for the smallest adult snail (including the shell) is 0.036 mm3. In the absence of extreme food specialization, miniaturization of land snails is probably driven by the accessibility of small spaces in the subsoil, although other scenarios, such as avoidance of larger predators, cannot be ruled out. The lower limit of adult shell size may be determined by the fact that it must accommodate at least one viable egg, the size of which in turn, may be limited by the minimum number of neurons to be functional in the hatchling. On the other hand, Angustopila coprologos n. sp. is characterized by a rough surface sculpture (most complex among all known and undescribed species of its genus), and minuscule mud granules arranged in radial lines on its shell surface. These granules may play a role in camouflage and mate recognition or function like mini sponges for water retention.
Barna Páll-Gergely, Adrienne Jochum, Jaap J. Vermeulen, Katja Anker, András Hunyadi, Aydin Örstan, Ábel Szabó, László Dányi and Menno Schilthuizen. 2022. The World’s Tiniest Land Snails from Laos and Vietnam (Gastropoda, Pulmonata, Hypselostomatidae). Contributions to Zoology. DOI: 10.1163/18759866-bja10025
