Tricula montana (Benson, 1843)

Gittenberger, Edmund, Leda, Pema, Wangchuk, Jigme, Gyeltshen, Choki & Bjoern Stelbrink,, 2020, The genera Erhaia and Tricula (Gastropoda, Rissooidea, Amnicolidae and Pomatiopsidae) in Bhutan and elsewhere in the eastern Himalaya, ZooKeys 929, pp. 1-17 : 11-14

Tricula montana (Benson, 1843) Figs 1 , 16-17

Melania (Tricula) montana Benson, 1843: 467 ( “Bhimtal”, Nainital District, Uttarakhand, India; 1370 m a.s.l.). Lectotype in The Natural History Museum, London no. 1964426 (design. Davis et al. 1986: 428, fig. 3A).

Tricula montana ; Preston 1915: 68. Davis et al. 1986: 428-433, figs 3-4 (shell), 4 (operculum), 5-8 (anatomy), 9-10 (radula). Nesemann et al. 2007: 62, 78 pl. 15, fig. 1.

Material examined.

Bhutan • District Lhuentse: Khardungchhu; 27°31'56"N, 91°12'19"E; 1634 m a.s.l.; J. Wangchuk leg. 28.IV.2017; 3 shells; NBCB 1061. Same data except for 27.III.2019; 8 specimens in ethanol 70%; NBCB 1064.

District Lhuentse: Jarkangchhu; 27°32'27"N, 91°12'25"E; 1333 m a.s.l.; J. Wangchuk leg. 28.IV.2017; 2 shells; NBCB 1063. Same data except for 27.III.2019; 7 specimens in ethanol 70%; NBCB 1066.

District Lhuentse: Songkhangchhu; 27°31'54"N, 91°11'17"E; 1152 m a.s.l.; J. Wangchuk leg. 27.III.2019; 3 specimens in ethanol 70%; NBCB 1068.

District Lhuentse: Fawan; 27°29'22"N, 91°10'57"E; 940 m a.s.l.; J. Wangchuk leg. 27.III.2019; 3 specimens in ethanol 70%; NBCB 1069.

District Mongar: Chhuburee; 27°15'41"N, 91°09 02"E; 818 m a.s.l.; J. Wangchuk leg. 3.V.2017; 2 shells; NBCB 1062. Same data except for 26.III.2019; 5 specimens in ethanol 70%; NBCB 1065.

District Mongar: Rekpalung; 27°19'34"N, 91°13'28"E; 885 m a.s.l.; J. Wangchuk leg. 27.III.2019; 3 specimens in ethanol 70%; NBCB 1070.

District Trongsa: Chendebji; 27°29'24"N, 90°20'18"E; 2631 m a.s.l., J. Wangchuk photographed 12.I.2018.

District Wangdue Phodrang: 40 km SSE of Wangdue Phodrang; 27°09'25"N, 90°04'05"E; 527 m a.s.l.; E. Gittenberger, Choki Gyeltshen & Kezang Tobgay leg. 24.IX.2019; 23 shells; 23 specimens in ethanol 70%; 10 specimens in ethanol 97%; NBCB 1084.

District Zhemgang, Kekhar, 27°12'37"N, 90°46'28"E; 1540 m a.s.l., J. Wangchuk leg. photographed 17.I.2018.

Shell.

Shell slender conical, with up to c. 5 shouldered, moderately convex whorls, separated by an incised suture; with obsolete growth lines and poorly discernible dense spiral lirae. Pale yellowish grey, with a light brown apertural border when fully grown. Apex not flattened, often decollate. Aperture triangular with broadly rounded edges, its parietal side about double the length of the columellar side; palatal side straight, passing into the slightly curved basal border with a more strongly curved transitional part. Parietal border of the aperture attached, at least in the middle and not or only slightly protruding. Umbilicus closed or nearly so.

Measurements.

According to Davis et al. (1986: 431) the shell height of males and females combined (N = 10) is 3.32-3.72 mm. However, for the lectotype a larger shell height is indicated, i.e. 3.92 mm ( Davis et al. 1986: 429, fig. 3A, 430). That shell is not even a relatively large specimen. Additional shells figured by Davis et al. (1986: 429, 430, fig. 3F, G, H, K, L) and printed at the same scale, are larger.

The shells that are known from Bhutan (N = 73) are relatively small, with 5- 5½ whorls measuring H 2.8-3.6 mm, B 1.3-1.7 mm.

Distribution.

(Fig. 1 ). According to Subba Rao (1989: 68) this species occurs in the Indian states of Himachal Pradesh ("Jhiri valley") and Uttarakhand (= Uttaranchal). Nesemann et al. (2007: 62) refers to it as widely distributed in the western and central Himalaya, in Nepal mainly at 1300-2100 m a.s.l. The records for Bhutan, at altitudes of 527-2631 m a.s.l., extend its range eastwards.

Habitat.

This species was found in Bhutan without accompanying Erhaia species mostly in densely vegetated, shaded areas with more or less overgrown springs and streamlets (Figs 1 , 13 - 15 ). Davis et al. (1986: 427) describe a similar habitat for the Nainital District near the type locality of T. montana . The locality in the district of Wangdue Phodrang is an overgrown, dripping wet, vertical, rocky wall along the road.

The shells from Mongar, Chhuburee, and from Lhuentse, Jarkangchhu, are all decollate (Fig. 17 ), whereas shells from the other localities still have their apical whorls present (Fig. 16 ). This might be a consequence of unknown differences in water quality at those different localities.

DNA data.

Two snails from Chhuburee and two snails from Khardungchhu were sequenced. These specimens shared the same haplotype per population for both 16S rRNA (GenBank acc. nos. MT239080 and MT239079, for Chhuburee and Khardungchhu,) and COI (GenBank acc. nos. MT237718 and MT237717, for Chhuburee and Khardungchhu). The two populations differed genetically by 1.0% and 4.9% for 16S rRNA and COI, respectively. Because the monophyly of Tricula remains uncertain (see e.g., Liu et al. 2014), we compared these sequences with additional data available from GenBank. For 16S rRNA, the lowest genetic distances, i.e., 3.1% and 3.3%, were identified between snails from Chhuburee and Khardungchhu, respectively, and Tricula sp. from China, Hunan, Xiangxi, Fenghuang (GenBank acc. no. EU311736), and 3.3% and 3.5% between snails from Chhuburee and Khardungchhu, respectively, and T. ludongbini Davis & Y.-H. Guo, 1986 from China, Yunnan, Panlong River, Hei Long Tan (GenBank acc. no. KC832717).

The genetic distances between T. montana from Chhuburee and Khardungchhu were considerably higher for COI, with 8.9% and 9.3%, respectively, between snails from Chhuburee and Khardungchhu and Tricula sp. from China, Sichuan, Dayi, Tian Gong Mia, Huang Ba (GenBank acc. no. AF253070), and Tricula hortensis Attwood & Brown, 2003 from China (GenBank acc. no. JQ082621).

Notes.

The species was identified conchologically by using the data provided by Benson (1843), Davis et al. (1986) and Nesemann et al. (2007), taking also the distributional data ( Nesemann et al. 2007: 62) into account.

Some species of Tricula may transmit schistosomes that could in principle infect humans and other mammals. No data in respect of this are known for T. montana .

See Davis et al. (1986) for a detailed account on this species, with data on shell morphology, anatomy of males and females, biogeography, and systematic relationships.

Figures

Figure 1. Records of the sympatric Erhaia jannei and E. pelkiae (star), E. wangchuki (triangle), and Tricula montana (dots) in Bhutan.

Figure 13. Habitat of Tricula montana; Bhutan, district Mongar, Chhuburee, 818 m a. s. l. Photo by JW.

Figure 15. Habitat of Tricula montana; Bhutan, district Lhuentse, Khardungchhu, 1634 m a. s. l. Photo by JW.

Figures 16, 17. Tricula montana (Benson, 1843), Bhutan 16 District Lhuentse, Khardungchhu, 1634 m a. s. l. (H 3.1 mm) 17 Bhutan, district Mongar, Chhuburee, 818 m a. s. l. (decollate specimen, H 3.0 mm). Photos by J. Goud.