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Research Article
Seven new hypselostomatid species from China, including some of the world’s smallest land snails (Gastropoda, Pulmonata, Orthurethra)
expand article infoBarna Páll-Gergely, András Hunyadi§, Adrienne Jochum|, Takahiro Asami
‡ Shinshu University, Matsumoto, Japan
§ Adria sétány 10G 2/5., Budapest 1148, Budapest, Hungary
| University of Bern & Naturhistorisches Museum der Bürgergemeinde Bern, Bern, Switzerland
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Abstract

Seven new species of Hypselostomatidae are described from the Chinese province Guangxi: Angustopila dominikae Páll-Gergely & Hunyadi, sp. n., A. fabella Páll-Gergely & Hunyadi, sp. n., A. subelevata Páll-Gergely & Hunyadi, sp. n., A. szekeresi Páll-Gergely & Hunyadi, sp. n., Hypselostoma socialis Páll-Gergely & Hunyadi, sp. n., H. lacrima Páll-Gergely & Hunyadi, sp. n. and Krobylos sinensis Páll-Gergely & Hunyadi, sp. n. The latter species is reported from three localities. All other new species are known only from the type locality. Specimens nearly identical to the type specimens of Angustopila huoyani Jochum, Slapnik & Páll-Gergely, 2014 were found in a cave in northern Guangxi, 500 km from the type locality. Adult individuals of Angustopila subelevata sp. n. (shell height = 0.83–0.91 mm, mean = 0.87 mm) and A. dominikae sp. n. (shell height of the holotype = 0.86 mm) represent the smallest known members of the Hypselostomatidae, and thus are amongst the smallest land snails ever reported. We note that Pyramidula laosensis Saurin, 1953 might also belong to Krobylos. Paraboysidia neglecta van Benthem Jutting, 1961, which was previously included in Angustopila, is classified in Hypselostoma.

Keywords

Taxonomy, land snail, dwarfism, Pupillidae, Vertiginidae, apertural barriers

Introduction

The term “microsnail” usually refers to gastropods with shells smaller than 5 mm (Panha and Burch 2005). Species within this size range do not form a monophyletic unit. Hence, the term “microsnail” is used in the practical sense only. Microgastropods represent a large portion of worldwide and tropical land snail diversity. Knowledge about their biodiversity is scant due to two main reasons: i) many microsnails are reported from caves only or known to inhabit rock outcrops, meaning that they can only be effectively collected using special techniques, such as sieving from soil samples; ii) many microsnails are reported from small ranges and often from the type locality only (e.g. Neubert and Bouchet 2015). However, microsnails can also tend to inhabit the broadest ranges known for land snails (e.g. Vertiginidae, Carychium; Nekola and Coles 2010, Weigand et al. 2013, Nekola 2014).

High rates of endemism amongst tropical microsnails requires researchers to perform detailed samplings over large geographic areas in order to find the narrow range endemic species. Superordinate systematics (genus and above) of small-shelled gastropods confronts similar difficulties. Since finding live populations is a challenging endeavour, classification is largely conchologically driven.

One of the families known to contain particularly tiny species is the family Hypselostomatidae, introduced by Zilch (1959) as a subfamily of Chondrinidae. The subfamily Aulacospirinae was also erected in the same work. Schileyko (1998a) synonymized these two taxa because no diagnostic characters were designated by Zilch (1959). The family Hypselostomatidae sensu Schileyko (1998a) inhabits Indochina, Indonesia, Australia and the Philippines, and contains the following genera: Boysidia Ancey, 1881 (with the subgenera Paraboysidia Pilsbry, 1917 and Dasypupa Thompson & Dance, 1983), Anauchen Pilsbry, 1917, Bensonella Pilsbry & Vanatta, 1900, Aulacospira Möllendorff, 1890, Pseudostreptaxis Möllendorff, 1890, Gyliotrachela Tomlin, 1930, Hypselostoma Benson, 1856, Campolaemus Pilsbry, 1892, Boysia L. Pfeiffer, 1849 and Acinolaemus Thompson & Upatham, 1997 (Schileyko 1998a). These genera, together with Systenostoma Bavay & Dautzenberg, 1909 are sometimes included in the Pupillidae (e. g. Panha and Burch 1999) or in theVertiginidae (e.g. Thompson and Upatham 1997). Schileyko (1998b) concluded that Systenostoma probably does not belong to Hypselostomatidae, but likely belongs to the Helicodiscidae due to the characteristic spiral sculpture. Later, he postulated that the genus is possibly related to Aulacospira as considered by Pilsbry (1917) or to Pupisoma Stoliczka, 1873 (Valloniidae) (Schileyko 2011). Jochum et al. (2014) renamed Systenostoma Bavay & Dautzenberg, 1909 (non Systenostoma Marsson, 1887, Bryozoa) as Tonkinospira Jochum, Slapnik & Páll-Gergely, 2014, and erected a new genus (Angustopila Jochum, Slapnik & Páll-Gergely, 2014) for some species which were previously classified within Systenostoma. Jochum et al. (2014) claimed that Angustopila probably belongs to the Hypselostomatidae, but the taxonomic position of Tonkinospira within the family remained uncertain. We include all genera in question (Angustopila, Hypselostoma, Krobylos Panha & Burch, 1999, Tonkinospira) in Hypselostomatidae.

In the present work, seven new species recently collected in Guangxi Province, China are described, belonging to the genera Angustopila, Hypselostoma and Krobylos. We also highlight some difficulties in the pre-existing practice of ranking species into genera based on conchological characters.

Materials and methods

Shells were first wetted in a dish of water and then manually brushed clean of mud using fine, tapered brushes, whereby each specimen was gently rotated back and forth between the brushes until it was sediment free. The shells were viewed without coating under a low vacuum SEM (Miniscope TM-1000, Hitachi High-Technologies, Tokyo). Shell whorl number was counted to the nearest quarter whorl according to Kerney and Cameron (1979).

Measurements of Angustopila and Hypselostoma specimens were taken from images obtained by a Nikon Digital Sight DS-FI1 microscope camera attached to a Nikon SMZ 800 Zoom Stereomicroscope. Krobylos specimens were measured using digital Vernier callipers. For the species descriptions, shell measurements are expressed as ratios such as SW/SH and AW/AH.

Abbreviations

HA Collection András Hunyadi (Budapest, Hungary)

HNHM Magyar Természettudományi Múzeum (Budapest, Hungary)

MNHN Muséum National d’Histoire Naturelle (Paris, France)

NMBE Naturhistorisches Museum der Burgergemeinde Bern, (Bern, Switzerland)

NHMUK The Natural History Museum (London, UK)

PGB Collection Barna Páll-Gergely (Mosonmagyaróvár, Hungary)

SMF Senckenberg Forschungsinstitut und Naturmuseum (Frankfurt am Main, Germany)

Taxonomic descriptions

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.

Including

concava (Thompson & Upatham, 1997), dominikae Páll-Gergely & Hunyadi, sp. n., elevata (Thompson & Upatham, 1997), huoyani Jochum, Slapnik & Páll-Gergely, 2014, fabella Páll-Gergely & Hunyadi, sp. n., subelevata Páll-Gergely & Hunyadi, sp. n., szekeresi Páll-Gergely & Hunyadi, sp. n., tamlod (Panha & Burch, 1999).

Remarks

Paraboysidia neglecta van Benthem Jutting, 1961 was classified within the genus Systenostoma by Panha and Burch and in Angustopila by Jochum et al. (2014) due to the presence of only two teeth in the aperture. The wide umbilicus and the detached peristome are, however, very similar to the members of the genus Hypselostoma (material examined: Caves near Biserat, state of Jalor, Malay Peninsula, NHMUK 1901.07.19.24–27, syntypes). Therefore we reclassify P. neglecta in Hypselostoma.

Angustopila dominikae Páll-Gergely & Hunyadi, sp. n.

Figure 1, 12

Type material

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E, leg. Hunyadi, A. & Szekeres, M., 10.09.2013., HNHM 99435 (holotype).

Diagnosis

A tiny, corpulent species with elongated aperture having a parietal and a single palatal tooth.

Description of the holotype

Shell minute, light grey, corpulent, almost globular, the penultimate whorl is the widest from apertural view; protoconch consists of 1.5 whorls, protoconch microstructure finely pitted and granular with a powdery superficial texture, the granular microstructure collectively radiates from the nuclear whorl and ceases at the second; teleoconch finely ornamented with irregularly-spaced radial growth lines crossed by fine rows of equidistantly spaced microscopic spiral threads; the 4.75 whorls are separated by a deep suture; whorls shouldered; aperture slightly oblique to shell axis; umbilicus deep, very narrow; aperture elliptical; the sinulus is narrow; peristome slightly expanded, not reflected; the mid section comprising the parietal tooth is sinuous and slightly protruding (in side view); parietal callus well developed, its portion between the parietal tooth and the columella adnate to the penultimate whorl; the portion of the callus between the parietal tooth and the upper right sinulus edge is detached; parietal tooth well developed with a very small additional tubercle (may be homologous with the angular tooth), the palatal tooth is positioned deeper in the shell and directly opposite the parietal tooth.

Figure 1.

Holotype of Angustopila dominikae Páll-Gergely & Hunyadi, sp. n. (HNHM 99435). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 0.86, SW = 0.8, AH = 0.3, AW = 0.37, SW/SH×100 = 93.02, AW/AH×100 = 123.33 (n = 1).

Differential diagnosis

Angustopila tamlod from Thailand also possesses two teeth (parietal and palatal), but it has a conical shell, which is nearly globular in A. dominikae sp. n. Moreover, A. tamlod has a narrower umbilicus and a more rounded aperture. Angustopila huoyani is larger than A. dominikae sp. n. It has a rather conical shell, more whorls, a narrower umbilicus, two apertural denticles and lacks the spiral thread-like lines (or has much weaker spiral striae) on the whole shell. The sympatric Angustopila subelevata sp. n. has a conical shell and lacks apertural dentition. See also under A. fabella sp. n. and A. szekeresi sp. n.

Etymology

The new species is named after Mrs. Dominika Páll-Gergely, the wife of the first author.

Type locality

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E.

Distribution

The new species is known from the type locality only (Figure 13).

Ecology

The single empty shell of this new species was found in a soil sample at the base of limestone rocks. It likely lives on limestone walls as do other similar hypselostomatid species recorded by Panha and Burch (2005).

Conservation status

A single empty shell has been collected from a soil sample at the type locality. Therefore, knowledge is very limited for evaluating its conservation status. Since the species is known from one site only, it is evaluated as Critically Endangered (CR) under IUCN criteria (IUCN 2014). Quarrying is quoted as the main threat to similar limestone habitats. However, no ongoing threats to the type locality are known at the moment.

Angustopila fabella Páll-Gergely & Hunyadi, sp. n.

Figure 2

Type material

China, Guangxi (广西), Chongzuo Shi (崇左市), Longzhou Xian (龙州县), cliffs north of Lenglei (楞垒), north of the Nonggang Nature Reserve (弄岗国家级自然保护区), 220 m, 22°29.161'N, 106°57.357'E, leg. Hunyadi, A. & Szekeres, M., 23.09.2013., HNHM 99436 (holotype), HNHM 99437/2 (figured paratypes), SMF 346520/1 paratype, HA/38 paratypes + 2 juvenile shells (not paratypes), PGB/1 paratype.

Diagnosis

A tiny, trigonal-shaped species with a rather rounded, slightly bean-shaped aperture bearing a well-developed parietal tooth.

Description

Shell minute, light grey, bluntly trigonal; protoconch consists of slightly more than 1.25 whorls, protoconch microstructure finely pitted and granular with a powdery superficial texture, the granular microstructure collectively radiates from the nuclear whorl and ceases at the second; teleoconch finely reticulate with irregularly-spaced radial growth lines crossed by rows of microscopic spiral threads; the 4.5–4.75 whorls are separated by a deep suture; whorls shouldered; aperture slightly oblique to shell axis; umbilical zone highly reticulate, umbilicus deep, relatively narrow; aperture heart-shaped; peristome slightly expanded, not reflected; parietal callus well-developed, very slightly adnate to the penultimate whorl; parietal tooth prominent, thick and long; no other dentition is present. Body whorl bulges beyond aperture (side view) by ca. 1/7 the max. breadth of the shell. Apertural lip tilted slightly back with fine creases behind the peristome (side view).

Figure 2.

Angustopila fabella Páll-Gergely & Hunyadi, sp. n. Holotype: (HNHM 99436: A, B, D, F), Paratype1 (HNHM 99437: E), Paratype2 (HNHM 99437: C, G, H). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 0.86–1.02, SW = 0.88–1, AH = 0.34–0.4, AW = 0.36–0.41 (n = 20). See also Tables 1 and 2.

Shell measurements (mm) for Angustopila fabella sp. n. from the type locality. SH: shell height, SW: shell width, AH: aperture height, AW: aperture width, SW/SH×100: shell width shared with shell height and multiplied by 100, AW/AH×100: aperture width shared with aperture height and multiplied by 100.

Specimen SH SW AH AW SW/SH×100 AW/AH×100
holotype 0.97 1 0.37 0.4 103.09 108.11
paratype1 0.96 0.98 0.39 0.41 102.08 105.13
paratype2 0.96 0.92 0.37 0.38 95.83 102.7
paratype3 1.01 0.94 0.37 0.38 93.07 102.7
paratype4 0.92 0.94 0.36 0.39 102.17 108.33
paratype5 0.86 0.98 0.4 0.4 113.95 100
paratype6 0.93 0.94 0.38 0.39 101.08 102.63
paratype7 0.97 0.93 0.39 0.39 95.88 100
paratype8 0.96 0.94 0.39 0.39 97.92 100
paratype9 0.99 0.89 0.36 0.39 89.9 108.33
paratype10 1.02 0.94 0.4 0.38 92.16 95
paratype11 0.92 0.93 0.37 0.4 101.09 108
paratype12 0.97 0.94 0.37 0.38 96.91 102.7
paratype13 0.97 0.93 0.37 0.4 95.88 108.11
paratype14 0.94 0.91 0.36 0.38 96.81 105.56
paratype15 0.93 0.88 0.34 0.37 94.61 108.82
paratype16 0.95 0.95 0.39 0.39 100 100
paratype17 0.89 0.89 0.35 0.36 100 102.86
paratype18 0.95 0.93 0.38 0.38 97.89 100
paratype19 0.93 0.91 0.37 0.39 97.85 105.41

Average, minimum value (min), maximum value (max), variance of values (var) and standard deviation of a set of values (stdev) for Angustopila fabella sp. n. (n = 20).

SH SW AH AW SW/SH×100 AW/AH×100
Average 0.95 0.9335 0.374 0.3875 98.4085 103.7195
Min 0.86 0.88 0.34 0.36 89.9 95
Max 1.02 1 0.4 0.41 113.95 108.82
Var 0.0014 0.0009 0.0003 0.0001 25.7841 14.9414
stdev 0.0376 0.0301 0.016 0.0116 5.0778 3.8654

Differential diagnosis

Angustopila fabella sp. n. is most similar to A. tamlod in shape and form. However, in addition to the parietal denticle, A. tamlod has a small, low palatal plica just opposite the parietal denticle. Angustopila dominikae sp. n. is smaller, has a globular shell (conical in A. fabella sp. n.) and possesses two apertural denticles with an additional tubercle on the parietal denticle. A single parietal denticle is present in A. fabella sp. n. See also A. subelevata sp. n. and A. szekeresi sp. n.

Etymology

The name, fabella, (Latin: little bean) refers to the bean-shaped aperture.

Type locality

China, Guangxi (广西), Chongzuo Shi (崇左市), Longzhou Xian (龙州县), cliffs north of Lenglei (楞垒), north of the Nonggang Nature Reserve (弄岗国家级自然保护区), 220 m, 22°29.161'N, 106°57.357'E.

Distribution

Angustopila fabella sp. n. is known from the type locality only (Figure 13).

Ecology

Empty shells of this new species were found in a soil sample at the base of large limestone rocks. It likely lives on limestone walls as do other similar hypselostomatid species recorded by Panha and Burch (2005).

Conservation status

Empty shells have been collected from a soil sample at the type locality. Therefore, knowledge is very limited for evaluating its conservation status. Since the species is known from one site only, it is evaluated as Critically Endangered (CR) under IUCN criteria (IUCN 2014). Quarrying is quoted as the main threat to similar limestone habitats. However, no ongoing threats to the type locality are known at the moment.

Angustopila huoyani Jochum, Slapnik & Páll-Gergely, 2014

Figure 3

Angustopila huoyani Jochum, Slapnik & Páll-Gergely, 2014: Jochum et al. 2014: 410: 27–29, Video 1, Figs 45.

Material examined

MNHN Expedition Nr. GX07.23.07, China, Guangxi (广西), Hechi (河池市), Huanjiang Xian (环江县), Midong village (米洞), Shui Dong (cave, 水洞), 23.05.2007, river sediment, alt. 332 m, 24.7485°N, 108.27191°E, leg. Franck Bréhier 12 shells (2 broken), NMBE 535121/3, SMF 341637/3, MNHN 2012-27046/4 + 2 broken shells).

Conservation status

This study reveals that A. huoyani inhabits two caves that are geographically far from each other. The typical threats to such habitats is quarrying and human disturbance through tourism.

Remarks

Angustopila huoyani has been described from a single cave in northeastern Hunan Province. Nearly identical shells have been found in another cave in northern Guangxi Province, which is situated ca. 500 km south from the type locality. The only difference is that the new shells have some very faint spiral striae on the teleoconch, which were not detected in the original population. This difference is, however, insufficient to distinguish these two populations on either specific or subspecific level. Therefore, we refer to the population collected in Guangxi as a disjunct population of A. huoyani. This finding underscores the need to explore more cave systems in order to make inferences about subterranean biodiversity in China, and specifically here for the distribution of minute troglobitic land snails.

Figure 3.

Angustopila huoyani Jochum, Slapnik & Páll-Gergely, 2014. Locality: Guangxi (广西), Hechi (河池市), Huanjiang Xian (环江县), Midong village (米洞), Shui Dong (cave, 水洞), 23.05.2007, river sediment, alt. 332 m, 24.7485°N, 108.27191°E. MNHN 2012-27046). All images: B. Páll-Gergely.

Angustopila subelevata Páll-Gergely & Hunyadi, sp. n.

Figure 4

Type material

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E, leg. Hunyadi, A. & Szekeres, M., 10.09.2013., HNHM 99438 (holotype), HNHM 99439/1 (paratype), HA/10 paratypes.

Diagnosis

A tiny, conical species with rounded or almost quadrangular aperture without dentition.

Description

Shell minute, light grey, conical with obtuse apex; spire tilted slightly left; protoconch consists of 1.25–1.5 whorls, microstructure finely pitted and granular with a powdery superficial texture, collectively radiating from the nuclear whorl; a prominent protoconch/teleoconch boundary is present (p/t), which is preceded by very faint rows of finely threaded microstructure; teleoconch finely reticulate with regularly-spaced radial growth lines crossed by rows of microscopic spiral threads.; on the last whorl, every 5th–6th radial line is stronger; the 4.25 whorls are separated by a deep suture; whorls shouldered; body whorl tumid; aperture slightly oblique to shell axis; umbilicus deep, relatively wide; aperture rounded or almost quadrangular, toothless; peristome slightly expanded, not reflected; parietal margin extends forward as a slight tongue-like projection along the columellar curvature; outer lip (side view) arched slightly and drawn back below suture.

Figure 4.

Holotype of Angustopila subelevata Páll-Gergely & Hunyadi, sp. n. (HNHM 99438). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 0.83–0.91, SW = 0.77–0.81, AH = 0.27–0.3, AW = 0.29–0.32 (n = 8). See also Tables 3 and 4.

Shell measurements (mm) for Angustopila subelevata sp. n. from the type locality. For abbreviations see Table 1.

Specimen SH SW AH AW SW/SH×100 AW/AH×100
holotype 0.88 0.8 0.3 0.31 90.91 103.33
paratype1 0.87 0.81 0.29 0.32 93.1 110.34
paratype2 0.86 0.77 0.3 0.32 89.53 106.67
paratype3 0.88 0.79 0.28 0.29 89.77 103.57
paratype4 0.85 0.78 0.3 0.32 91.76 106.67
paratype5 0.91 0.79 0.27 0.31 86.81 114.81
paratype6 0.86 0.79 0.3 0.31 91.86 103.33
paratype7 0.83 0.81 0.3 0.3 97.59 100

Average, minimum value (min), maximum value (max), variance of values (var) and standard deviation of a set of values (stdev) for Angustopila subelevata sp. n. (n= 8). For abbreviations see Table 1.

SH SW AH AW SW/SH×100 AW/AH×100
Average 0.8675 0.7925 0.2925 0.31 91.4163 106.09
Min 0.83 0.77 0.27 0.29 86.81 100
Max 0.91 0.81 0.3 0.32 97.59 114.81
Var 0.0006 0.0002 0.0001 0.0001 9.8582 21.9211
stdev 0.0238 0.0139 0.0116 0.0107 3.1398 4.682

Differential diagnosis

The most similar species is the Thai Angustopila elevata, which has a more slender shell, a deeper umbilicus and lacks the spiral striae on its base. A. fabella sp. n. has a wider shell, a stronger peristome and a well-developed parietal tooth, whereas A. subelevata sp. n. is toothless. See also the two sympatric species, A. dominikae sp. n. and A. szekeresi sp. n.

Etymology

The name, subelevata, refers to the similarity to the Thai Angustopila elevata.

Type locality

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E.

Distribution

The new species is known from the type locality only (Figure 13).

Ecology

As for Angustopila fabella sp. n.

Conservation status

As for Angustopila fabella sp. n.

Remarks

Angustopila elevata, which is known from approx. 1,000 km from the type locality of A. subelevata sp. n., is strikingly similar to the new species, although the general shell shape and the sculpture seem to be reliably different. See also Discussion.

Angustopila szekeresi Páll-Gergely & Hunyadi, sp. n.

Figure 5

Type material

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E, leg. Hunyadi, A. & Szekeres, M., 10.09.2013., HNHM 99440 (holotype), HNHM 99441/2 (one of them is a figured paratype), HA/6 paratypes.

Diagnosis

A tiny, trigonal species with rounded aperture having a weak parietal tooth.

Description

Shell minute, light grey, blunt trigonal; protoconch consists of 1.25 whorls, microstructure finely pitted and granular with a powdery superficial texture, collectively radiating from the nuclear whorl; spiral threads of microstructure transverse the protoconch as well as the teleoconch, a prominent protoconch/teleoconch boundary is present (p/t), which interrupts the very faint rows of finely threaded microstructure; teleoconch finely reticulate with regularly-spaced radial growth striations crossed by rows of microscopic spiral threads; every 8th–10th radial line is stronger and visible as growth ridges; the 4–4.25 whorls are separated by a deep suture; whorls rounded; aperture oblique to shell axis; umbilicus deep, relatively narrow; aperture rounded; peristome slightly expanded, not reflected; laterally viewed, the middle section is slightly protruding; parietal callus weak, adnate; parietal tooth weak but present in all specimens.

Figure 5.

Angustopila szekeresi Páll-Gergely & Hunyadi, sp. n. Holotype (HNHM 99440: A, C, D, E, F, G, H), Paratype (HNHM 99441: B). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 0.88–1.03, SW = 0.77–0.89, AH = 0.33–0.37, AW = 0.35–0.39 (n = 6). See also Tables 5 and 6.

Shell measurements (mm) for Angustopila szekeresi sp. n. from the type locality. For abbreviations see Table 1.

Specimen SH SW AH AW SW/SH×100 AW/AH×100
Holotype 0.91 0.8 0.34 0.36 87.91 105.88
paratype1 0.93 0.77 0.33 0.35 82.8 106.06
paratype2 1.03 0.89 0.36 0.39 86.41 108.33
paratype3 0.88 0.81 0.37 0.35 92.05 94.59
paratype4 1.03 0.85 0.36 0.39 82.52 108.33
paratype5 0.95 0.8 0.34 0.36 84.21 105.88

Average, minimum value (min), maximum value (max), variance of values (var) and standard deviation of a set of values (stdev) for Angustopila szekeresi sp. n. (n = 6). For abbreviations see Table 1.

SH SW AH AW SW/SH×100 AW/AH×100
Average 0.955 0.82 0.35 0.3667 85.9833 104.845
Min 0.88 0.77 0.33 0.35 82.52 94.59
Max 1.03 0.89 0.37 0.39 92.05 108.33
Var 0.0039 0.0018 0.0002 0.0003 13.1943 26.6148
stdev 0.0625 0.0429 0.0155 0.0186 3.6324 5.159

Differential diagnosis

Sympatric species. Angustopila subelevata sp. n. lacks a parietal tooth, it has a wider umbilicus, a smaller aperture, and its peristome is not adnate. Moreover, the spiral lines on the embryonic whorls are much weaker in A. subelevata sp. n. Angustopila dominikae sp. n. is smaller, has a much more corpulent shell and two teeth in the aperture. Hypselostoma socialis sp. n. is much larger and has four teeth in its aperture.

Non-sympatric species. Angustopila fabella sp. n. has a wider shell, a wider umbilicus, weaker spiral lines on its umbilicus, a stronger parietal tooth and a strong parietal callus (its peristome is not adnate).

Etymology

Angustopila szekeresi sp. n. is named after Miklós Szekeres, our friend and partner in the field work resulting in all new species reported in this paper.

Type locality

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E.

Distribution

The new species is known from the type locality only (Figure 13).

Ecology

As for Angustopila fabella sp. n.

Conservation status

As for Angustopila fabella sp. n.

Remarks

The spiral threading on the protoconch is common in the Hypselostomatidae (Panha and Burch 2005). Noteworthy, is the transition with the p/t boundary in that the microstructure continues in sync with the subsequent whorls. Normally, this phase of ontogenetic development in gastropods [p/t boundary] indicates the transition from the protoconch embryonal stage, whereby the shell structure changes and continues in the teleoconch constructional phase. The continuous protoconch-teleoconch microstructural condition here suggests likely progenesis in these snails.

Hypselostoma Benson, 1856

Hypselostoma Benson, 1856b; The Annals and Magazine of Natural History, ser. 2, no. 17: 342. (nomen novum pro Tanystoma Benson 1856a, non Motschulsky, 1845, Carabidae, Coleoptera).

Type species

Tanystoma tubiferum Benson, 1856a, by monotypy.

Remarks

See under the genus Angustopila.

Hypselostoma lacrima Páll-Gergely & Hunyadi, sp. n.

Figures 6, 8F–K

Type material

China, Guangxi (广西), Chongzuo Shi (崇左市), Longzhou Xian (龙州县), cliffs N of Lenglei (楞垒), N of the Nonggang Nature Reserve (弄岗国家级自然保护区), 220 m, 22°29.161'N, 106°57.357'E, leg. Hunyadi, A. & Szekeres, M., 23.09.2013., HNHM 99444 (holotype), HNHM 99445 (figured paratype), HA/2 paratypes.

Diagnosis

Shell conical, with tumid body whorl and deep umbilicus; aperture with sinulus vertically oriented; tubus detached; aperture with one parietal lamella, one columellar and two palatal teeth; parietal lamella long and nearly straight.

Description

Shell minute, whitish/light grey, conical with enlarged body whorl; protoconch consists of 1.5 or slightly less whorls, finely granulated, with at least six fine spiral striations; teleoconch reticulated and regularly spirally striated with strong, irregular radial lines; the 5.5 or slightly less whorls are separated by a deep suture; whorls sloping and rounded; aperture oblique to shell axis; base of shell broadly umbilicate due to lateral expansion of last whorl; aperture detached from the penultimate whorl; aperture with sinulus vertically oriented (from apertural view); peristome expanded, not reflected, with relatively sharp edge; four apertural barriers; only the angulo-parietal lamella reaches the peristome; angulo-parietal lamella very long and high, not interrupted; it is lowest near the peristome; its posterior (inner) end is not visible in frontal view; its anterior end (closest to the peristome) is bent toward the upper palatal plica, and its posterior end is bent toward the lower palatal plica; columellar and upper palatal folds elevated but short; the posterior end of the upper palatal fold curls toward the lower palatal fold; the lower palatal fold is also well-developed, and shorter than the others.

Figure 6.

Hypselostoma lacrima Páll-Gergely & Hunyadi, sp. n. Holotype (HNHM 99442: A, C–H), Paratype (HNHM 99445: B). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 1.33–1.35, SW = 1.34–1.35, AH = 0.45–0.51, AW = 0.44–0.5 (n = 2). See also Tables 7 and 8.

Shell measurements (mm) for Hypselostoma lacrima sp. n. from the type locality. For abbreviations see Table 1.

Specimen SH SW AH AW SW/SH×100 AW/AH×100
holotype 1.33 1.35 0.45 0.44 101.5 125.71
paratype 1.35 1.34 0.51 0.5 99.26 98.04

Average, minimum value (min), maximum value (max), variance of values (var) and standard deviation of a set of values (stdev) for Hypselostoma lacrima sp. n. (n = 2). For abbreviations see Table 1.

SH SW AH AW SW/SH×100 AW/AH×100
Average 1.34 1.345 0.48 0.47 100.38 111.875
Min 1.33 1.34 0.45 0.44 99.26 98.04
Max 1.35 1.35 0.51 0.5 101.5 125.71
Var 0.0002 0.0001 0.0018 0.0018 2.5088 382.8144
stdev 0.0141 0.0071 0.0424 0.0424 1.5839 19.5656

Differential diagnosis

See under Hypselostoma socialis sp. n.

Etymology

The name lacrima (Latin: tear) refers to the shape of the aperture.

Type locality

China, Guangxi (广西), Chongzuo Shi (崇左市), Longzhou Xian (龙州县), cliffs N of Lenglei (楞垒), N of the Nonggang Nature Reserve (弄岗国家级自然保护区), 220 m, 22°29.161'N, 106°57.357'E.

Distribution

The new species is known from the type locality only (Figure 13).

Ecology

As for Angustopila fabella sp. n.

Conservation status

As for Angustopila fabella sp. n.

Remarks

The subdivision of Hypselostomatidae is strongly based on the morphology of the apertural barriers (“teeth”). The main characters used for delimiting some of the major genera include the formation of the two teeth on the parietal region of the aperture, namely the parietal tooth (lamella) or parietalis and the angular tooth (lamella) or angularis. Gyliotrachela, Paraboysidia and Acinolaemus are said to possess separate parietal and angular lamellae. The former two have a more prominent parietal lamella rather than angular lamella, but in Acinolaemus, the angular is the dominant tooth. The angular lamella is entirely missing in the genus Anauchen. In the genera Hypselostoma and Boysidia these two lamellae are fused (Pilsbry 1917, Thompson and Upatham 1997, Panha and Burch 2005). Sometimes it is challenging to ascertain whether we are dealing with a single lamella (homologous with the parietal lamella) having a bifid anterior end or two lamellae (parietal and angular), which are concrescent. Moreover, the genera Hypselostoma and Gyliotrachela did not form monophyletic units in the molecular phylogeny presented by Tongkerd et al. (2004), suggesting that the key characters used in classic taxonomy have developed phenotypically plastic forms. In this case of the two new species (Hypselostoma lacrima sp. n. and H. socialis sp. n.), we interpret the lamella on the parietal apertural wall as a congruent angulo-parietal lamella. Hence, both species are placed in Hypselostoma.

Hypselostoma socialis Páll-Gergely & Hunyadi, sp. n.

Figures 7, 8A–E

Type material

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E, leg. Hunyadi, A. & Szekeres, M., 10.09.2013., HNHM 99442 (holotype), HNHM 99443/3 (figured paratypes), SMF 346521/1 paratype, HA/15 paratypes + 4 juvenile shells (not paratypes), PGB/1.

Diagnosis

Shell spire conical, shell turban-shaped with tumid body whorl and broadly set, deep umbilicus; tubus detached; aperture rounded with wide sinulus, the upper parietal lamella dips to the right; aperture with a parietal lamella, one columellar and two palatal teeth; parietal lamella long and depressed, Z-shaped.

Description

Shell minute, whitish/light grey, conical with enlarged body whorl; protoconch consists of 1.5 whorls, finely pitted, with very slight indication of spiral lines; teleoconch reticulated with fine, regularly spirally striate microstructure intersected with irregular radial lines; the 5.5 whorls are separated by deep suture; whorls horizontally positioned, rounded; aperture oblique to shell axis; umbilicus deep, wide, especially at the last whorl; aperture free from the penultimate whorl, rounded with wide sinulus (area isolated by the parietal and upper palatal lamellae); sinulus horizontally oriented (apertural view); peristome slightly expanded, not reflected, with relatively sharp edge; (side view), the horizontally directed tuba is deflected downwards in alignment with the body whorl; four teeth recessed within aperture; only the ridge-like angulo-parietal lamella reaches the peristome, the others are situated deeper; angulo-parietal lamella moderately long, its end is visible from a straight view into the aperture; it is interrupted, consisting of an anterior section (situated closer to the peristome) and a slightly longer posterior section (situated deeper in the aperture); the anterior section is strongly bent toward the sinulus, its tip nearly touches the tip of the upper palatal fold; the posterior part of the angulo-parietal lamella is less strongly bent than the anterior portion, only its anterior part is bent toward the upper palatal lamella; the angulo-parietal and the upper palatal lamellae follow each other; the angulo-parietal lamella has a depressed Z-shape when observed after breaking off the lower part of the aperture; the anterior part of the angulo-parietal lamella is possibly homologous with the parietal lamella of other hypselostomatid taxa, while the second portion might be homologous with the angular lamella, or vice versa; columellar and lower palatal lamellae are elevated, blunt and short, they are about the same length and are visible through the semi-transparent shell; the upper palatal fold is also of similar length, its posterior end runs parallel with the lower palatal fold; the tip of the upper palatal fold nearly touches the tip of the angulo-parietal lamella.

Figure 7.

Holotype of Hypselostoma socialis Páll-Gergely & Hunyadi, sp. n. (HNHM 99442). All images: B. Páll-Gergely.

Figure 8.

Aperture and apertural barriers of Hypselostoma species. A–E Hypselostoma socialis sp. n.: Holotype (HNHM 99442: A) Paratype1 (HNHM 99443: B, E), Paratype2 (HNHM 99443: C), Paratype3 (HNHM 99443: D); F–K Hypselostoma lacrima sp. n.: Holotype (HNHM 99444: F–I), Paratype (HNHM 99445: J–K). All images: B. Páll-Gergely.

Measurements

(in mm): SH = 1.14–1.34, SW = 1.22–1.36, AH = 0.43–0.5, AW = 0.49–0.53 (n = 10). See also Tables 9 and 10.

Shell measurements (mm) for Hypselostoma socialis sp. n. from the type locality. For abbreviations see Table 1.

Specimen SH SW AH AW SW/SH×100 AW/AH×100
holotype 1.34 1.36 0.46 0.51 101.49 110.87
paratype1 1.25 1.31 0.43 0.5 104.8 116.28
paratype4 1.22 1.28 0.46 0.5 104.92 108.7
paratype5 1.21 1.27 0.47 0.5 104.96 106.38
paratype6 1.22 1.26 0.45 0.49 103.28 108.89
paratype7 1.23 1.26 0.48 0.51 102.44 106.25
paratype8 1.18 1.22 0.45 0.49 103.39 108.89
paratype9 1.14 1.28 0.45 0.51 112.28 113.33
paratype10 1.26 1.31 0.5 0.53 103.97 106
paratype11 1.21 1.3 0.47 0.53 107.44 112.77

Average, minimum value (min), maximum value (max), variance of values (var) and standard deviation of a set of values (stdev) for Hypselostoma socialis sp. n. (n = 10). For abbreviations see Table 1.

SH SW AH AW SW/SH×100 AW/AH×100
Average 1.226 1.285 0.462 0.507 104.897 109.836
Min 1.14 1.22 0.43 0.49 101.49 106
Max 1.34 1.36 0.5 0.53 112.28 116.28
Var 0.0028 0.0014 0.0004 0.0002 9.3754 11.7788
stdev 0.0526 0.0378 0.0193 0.0142 3.0619 3.432

Differential diagnosis

Hypselostoma lacrima sp. n. and H. socialis sp. n. are the only species of Hypselostoma known from China. Some Chinese species formerly included in Hypselostoma have been reassigned to other genera (Yen 1939). Hypselostoma dilatatum Benthem Jutting 1962, H. rupestre Benthem Jutting 1962 and H. annamiticum Möllendorff, 1900 are approximately two times larger than H. lacrima sp. n. and H. socialis sp. n., and have more (5–8) apertural barriers. Hypselostoma laidlawi from Malaysia is similar in size to H. lacrima sp. n. and H. socialis sp. n., but it has a much narrower umbilicus and five apertural barriers.

Hypselostoma lacrima sp. n. has a much wider umbilicus than H. socialis sp. n. Moreover, the spiral lines on the protoconch of H. socialis sp. n. are weaker than those of the other species. The aperture of H. lacrima sp. n. is heart-shaped with the sinulus vertically oriented, whereas the aperture of H. socialis sp. n. is semi-quadrate and rounded with its sinulus positioned horizontally. The parietal lamella of Hypselostoma socialis sp. n. is interrupted and short (depressed Z-shaped), whereas that of H. lacrima sp. n. is longer and straighter, lacking the conspicuous blade-like ridge visible in H. socialis sp. n.

Etymology

The name, socialis, (Latin: social) refers to the fact that this new species has been found together with three Angustopila species.

Type locality

China, Guangxi (广西), Hechi Shi (河池市), Bama Xian (巴马县), cliffs at the southern edge of Jiaole Cun (交乐村), 590 m, 24°7.045'N, 107°7.847'E.

Distribution

Hypselostoma socialis sp. n. is known from the type locality only (Figure 13).

Ecology

As for Angustopila fabella sp. n.

Conservation status

As for Angustopila fabella sp. n.

Remarks

See under Hypselostoma lacrima sp. n.

Krobylos Panha & Burch, 1999

1999 Krobylos Panha & Burch, Walkerana 10 (24): 127.

Type species

Krobylos pomjuk Panha & Burch, 1999, by original designation.

Krobylos sinensis Páll-Gergely & Hunyadi, sp. n.

Figures 9, 10

Type material

China, Guangxi (广西), Bose Shi (百色市), Leye Xian (乐业县), Chuandong Tiankeng Scenic Area (穿洞天坑景区), inner cliffs of the dolina, 1290 m, 24°48.430'N, 106° 29.277'E, leg. Hunyadi, A. & Szekeres, M., 09.09.2013., HNHM 99446 (holotype), HNHM 99447/1 (paratype), SMF 346522/1 paratype, HA/12 paratypes + 2 juvenile shells (not paratypes), PGB/1; China, Guangxi (广西), Hechi Shi (河池市), Tiane Xian (天峨县), Qimu Xiang (豈暮乡), cross towards Lahao Yan (拉号岩), 600 m, 24°51.130'N, 107°11.670'E, leg. Hunyadi, A. & Szekeres, M., 12.09.2013., HA/3 paratypes; China, Guangxi (广西), Hechi Shi (河池市), Huanjiang Xian (南丹县), cliffs above Dongning (峒宁) Village S of the Mulun Nature Reserve (木论国家级自然保护区), 530 m, 25°5.970'N, 107°57.639'E, leg. Hunyadi, A. & Szekeres, M., 17.09.2013., HA/3 paratypes.

Diagnosis

A large Krobylos species with conical spire, rounded, regularly coiled whorls, large oval-shaped aperture, adnate parietal side and very weak indication of spiral striae on its dorsal surface.

Description

Shell small, usually wider than high, only a single specimen from the Mulun Nature Reserve had the shell height and the shell diameter both measuring 2.7 mm; the 3.75–4.25 whorls are separated by a well-defined deep suture; whorls weakly angular, especially the penultimate whorl; protoconch light brownish purple, glossy, no notable sculpture visible; teleoconch light to dark purple, or pinkish, with blunt, irregularly course wrinkles; no spiral lines are visible under the microscope, but the SEM images revealed a hint of spiral striation on the lower half of each whorl (except for the last one); umbilicus open, narrow, (from ventral view), only its edge is covered by the peristome; aperture wide with its parietal part adnate to the penultimate whorl; peristome sharp, not thickened, not expanded nor reflexed; aperture reflected at columellar margin such that it covers the edge of the umbilicus.

Figure 9.

Holotype of Krobylos sinensis Páll-Gergely & Hunyadi, sp. n. (HNHM 99446). All images: B. Páll-Gergely.

Figure 10.

Sculpture of the holotype of Krobylos sinensis sp. n. (HNHM 99446). Abbreviations: NS: no spiral lines; S: spiral lines present. All images: B. Páll-Gergely.

Measurements

(in mm): SH = 2.2–2.7, SW = 2.5–3 (n = 13 from all populations).

Differential diagnosis

Krobylos sinensis sp. n. differs from Tonkinospira depressa (Jaeckel 1950) by the larger size, rounded whorls and the absence of spiral sculpture on the upper sides of the whorls. The aperture of Tonkinospira defixa (Bavay & Dautzenberg, 1912) is not adnate, and its shell is much smaller than K. sinensis sp. n. Tonkinospira pulverea (Bavay & Dautzenberg, 1909) has more rounded whorls and the entire surface is regularly spirally striated. Tonkinospira pauperrima (Bavay & Dautzenberg, 1909) has a much more elevated spire, narrower umbilicus and stronger spiral striae.

Krobylos maehongsonensis Panha & Burch, 1999 has a higher spire, a relatively larger aperture, sharper keel, weaker radial growth lines and more bulging whorls from dorsal view (in K. sinensis sp. n. the whorls are ventrally more flat). Krobylos kangkoy Panha & Burch, 2004 (in Panha et al. 2004) has a much narrower umbilicus than the new species. Krobylos pomjuk Panha & Burch, 1999 also has a narrower umbilicus and a more depressed shell with a wider aperture. It is much smaller than K. sinensis sp. n. Similarly as small, Krobylos takensis Panha & Burch, 2004 (in Panha et al. 2004) has a higher spire and more angled whorls. Krobylos tampla is even smaller bearing a narrower umbilicus. The aperture of Krobylos veruwan Panha & Burch, 2004 (in Panha et al. 2004) has a low palatal ridge, which is missing in K. sinensis sp. n. Moreover, K. veruwan is much smaller than K. sinensis sp. n. and has a narrower umbilicus. Pyramidula laosensis Saurin 1953, which also likely also belongs to Krobylos, shows increased bulging whorls and a more pronounced closure of the umbilicus by the peristome.

Etymology

The species is named after China, the country of its type locality.

Type locality

China, Guangxi (广西), Bose Shi (百色市), Leye Xian (乐业县), Chuandong Tiankeng Scenic Area (穿洞天坑景区), inner cliffs of the dolina, 1290 m, 24°48.430'N, 106° 29.277'E.

Distribution

Krobylos sinensis sp. n. has been found in three different localities in northern Guangxi Province (Figure 13). See also remarks on the distinctness of Krobylos and Tonkinospira.

Ecology

Empty shells of this new species have been found in a soil sample at the base of large limestone rocks. It probably lives under stones and inside crevices.

Conservation status

Krobylos sinensis sp. n. is reported from three sites in this study. This species may inhabit similar habitats in the same geographic area. At the moment, on a global scale, its distribution is likely limited to less than 5 sites, therefore these vulnerable narrow range endemics warrant conservation priority (Vu D2) in conjunction with the Guidelines for the IUCN Red List (IUCN Standards and Petitions Subcommittee 2014).

Remarks

Krobylos was described as a group of toothless snails entirely lacking superficial microstructure (Panha and Burch 1999). Tonkinospira, on the other hand, has prominent spiral microsculpture over the entire surface. In this respect, Krobylos sinensis sp. n. is intermediate, because it has only very slight indication of spiral striae on the lower half of the whorls. This spiral sculpture is very faint or not visible under the microscope, but detectable using SEM images. We provisionally place K. sinensis sp. n. in the genus Krobylos because of the very weak spiral striae. However, we remark that the distinctness of the genera Krobylos and Tonkinospira requires further study. Krobylos sinensis sp. n. is the only species assigned to Krobylos reported outside of Thailand. However, “Pyramidulalaosensis might also belong to the same genus.

Discussion

Some of the new species reported in this study, especially the member of the genus Angustopila, have remarkably tiny shells. Adult individuals of Angustopila subelevata sp. n. (shell height = 0.83–0.91 mm, mean = 0.87 mm) and A. dominikae sp. n. (shell height of the holotype = 0.86 mm) represent the smallest members of the genus Angustopila, since the smallest member of the genus so far was Angustopila elevata with 0.92–0.99 mm height (Thompson and Upatham 1997) (Figure 11).

Figure 11.

Comparison of the sizes of the five smallest Angustopila species. A Angustopila fabella sp. n. B Angustopila szekeresi sp. n. C Angustopila elevata D Angustopila subelevata sp. n. E Angustopila dominikae sp. n. Dark grey silhouettes represent the smallest, light grey the largest shells. The numbers above the shells indicate the number of shells measured.

Figure 12.

The holotype of Angustopila dominikae sp. n. in the eye of a sewing needle to picture its extraordinary small size. Photo: B. Páll-Gergely and N. Szpisjak.

Figure 13.

Map showing the distributions of newly described species of Chinese Hypselostomatidae. Filled circle: Krobylos sinensis Páll-Gergely & Hunyadi, sp. n. 1 Type locality of Angustopila huoyani 2 new locality of Angustopila cf. huoyani 3 Type locality of Angustopila dominikae Páll-Gergely & Hunyadi, sp. n., Angustopila subelevata Páll-Gergely & Hunyadi, sp. n., Angustopila szekeresi Páll-Gergely & Hunyadi, sp. n. and Hypselostoma socialis Páll-Gergely & Hunyadi, sp. n. 4 Type locality of Angustopila fabella Páll-Gergely & Hunyadi, sp. n. and Hypselostoma lacrima Páll-Gergely & Hunyadi, sp. n.

During a non-exhaustive literature survey (Powell 1979, Schileyko 1998a, 1998b, 2002, Panha and Burch 2005 for pulmonates; Boeters et al. 1989, Panha and Burch 2005, Liew et al. 2014 for operculate land snails), we found only very few reports of species smaller than 1 mm. The smallest land snail presented in these literature is “Pupisoma sp.” from Thailand, measuring “about 0.9 mm in length” (Panha and Burch 2005). Only a few genera containing species smaller than 1.5 mm according to Schileyko (1998a, 1998b, 2002), for example: Pupisoma (H = 1.3–3 mm; Schileyko 1998a), Salpingoma Haas 1937 (H = 1.3–1.5 mm; Schileyko 1998a), Truncatellina Lowe, 1852 (H = 1.2–2.5; Schileyko 1998b), Acinolaemus (H = 0.87–1.61, D = 0.65–1.92; Schileyko 1998b, page 255) and Punctum Morse, 1864 (D = 1–2 mm; Schileyko 2002). The height of 0.87 mm in Acinolaemus refers to a paratype of Acinolaemus colpodon Thompson & Upatham, 1997 measured from the base of the last whorl to the apex, but this is not the largest diameter of that shell. The largest measurement of that paratype is 1.05 mm from the base of the last whorl to the aperture. The diameter of 0.65 mm probably refers to the aperture height of A. rhamphodon Thompson & Upatham 1997, which appears as a measurement of the shell width due to the shifting of data in the table presented in the original description (Thompson and Upatham 1997, page 227). Paralaoma serratocostata Webster, 1906, which is probably the smallest land snail in New Zealand, is generally less than 1.0 mm maximum shell dimension over a large part of its range (Powell 1979), but in some areas can reach 0.7 × 1.2 mm (Gary M. Barker, pers. comm.). As for operculated land snails, Liew et al. (2014) mentioned that the genus Plectostoma Adams, 1865 has a shell height of 1.0–3.7 mm. Platyla minutissima Boeters, Gittenberger & Subai, 1989, which is mentioned as the smallest European land snail, has a shell height of 1.1–1.25 mm. These data suggest that Angustopila subelevata sp. n. and A. dominikae sp. n. are amongst the smallest land snails ever reported if the largest measurement of the shell is considered. If however, shell volume is calculated according to McCain and Nekola (2008) and Nekola (2014), there are even tinier land snails (e.g. Punctidae spp) occupying the lowest rung of the volume/size scale.

The smallest snails are, however, certainly marine species. The smallest recorded gastropod seems to be Ammonicera minortalis Rolán, 1992, ranging in size from 0.32 to 0.46 mm. Although a few marine species less than 1 mm are known, all of them are larger than A. minortalis. For example, Europe’s smallest gastropod, Retrotortina fuscata Chaster, 1896 measures 0.5–0.75 mm (Gofas and Warén 1998). Extremes in body size of organisms not only attract attention from the public, but also incite interest regarding their adaptation to their environment (Hanken and Wake 1993, Grebennikov 2008, Glaw et al. 2012). Investigating tiny-shelled land snails is important for assessing biodiversity and natural history as well as for establishing the foundation for studying the evolution of dwarfism in invertebrate animals. The present data are insufficient for addressing the evolutionary processes of miniaturization in land snails. However, we hope that these results provide the taxonomic groundwork for future studies concerning the evolution of dwarfism in invertebrates.

Biogeography

The similarity between distantly distributed species (A. elevataA. subelevata; A. tamlodA. huoyani) and the two populations of Angustopila huoyani can be explained by three different hypotheses: (1) These populations may be connected with additional populations (i.e. via contiguous cave systems or interconnected river drainage basins) resulting in a continuous distributional area. The 500–1000 km gap between the known populations is therefore due to lack of additional exploration and thus, additional material; (2) they can be the results of rare long distance dispersal events; or (3) convergent evolution of shell traits. Our present knowledge is insufficient to reject any of these hypotheses.

Acknowledgements

We thank Louis Deharveng (MNHN) for providing us valuable A. huoyani material and Katsura Yamada (Shinshu University) for helping us measure the shells. Our gratitude goes to Ronald Janssen (SMF) and Jonathan Ablett (NHMUK) for assistance in accessing their museum collections. We acknowledge Aydın Örstan and Emmanuel Tardy (MHNG, Geneva, Switzerland) for providing information and literature, to Nikolett Szpisjak (University of Szeged) for her help in photographing the material, and to Gary M. Barker for providing valuable information. We thank the reviewers, Jeff Nekola and John Stanisic for their helpful input on earlier version of the manuscript. The first author is grateful to the László Körmöczi and Zsolt Pénzes of the Department of Ecology, University of Szeged for their kind assistance in opening their laboratory and providing equipment during his stay in Szeged. We are indebted to The Biodiversity Heritage Library for the multitude of rare literature made available to us (www.biodiversitylibrary.org). This study was supported by scholarships from Japan Student Services Organization and Mitsubishi Corporation to BPG and Grants-in-Aid from Japan Society for the Promotion of Science to TA.

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