Erhaia Davis & Kuo (Gastropoda, Rissooidea, Amnicolidae) also in Bhutan

Abstract The occurrence of at least one species of Erhaia in Bhutan, viz. Erhaia wangchuki sp. n., is confirmed by DNA sequencing. A second unnamed species from Bhutan, that might be congeneric, is known from only a single shell. According to the molecular analysis, E. wangchuki is most closely related to a still undescribed Erhaia species from China. These two species together with E. jianouensis and Akiyoshia kobayashii, both also from China, form a well supported clade. Awaiting additional molecular data, the apparent inconsistency regarding Erhaia versus Akiyoshia is not dealt with here. The extant true sister species of E. wangchuki could be among the four SE Himalayan species from Bhutan and Nepal that are classified with Erhaia on the basis of conchological data only.


Introduction
The extremely speciose superfamily Rissooidea, with over 400 recent genera 'one of the largest gastropod families' (Wilke et al. 2001: 1), encompasses very many species that cannot be identified on the basis of only shell characters, distribution and ecology. Anatomical characters may additionally be used, when the equipment for dissection is available, but even that technically demanding approach does not always bring conclusive results. Therefore, molecular analyses are advisable in cases like this. This has resulted in a more reliable classification allowing these snails to be used as ecological indicator species on the one hand and model organisms in historical biogeography on the other hand.
After its description by Davis and Kuo in Davis et al. (1985), the genus Erhaia turned out to be widespread in Asia. From Nepal, two species of Erhaia are reported by Nesemann et al. (2007) on the basis of shell shape and ecology. Here, we report the occurrence of a species of Erhaia in Bhutan, confirmed by a molecular analysis. The shell of a species that might be congeneric is additionally described but without naming it.

Material and methods
The first author coincidentally collected a minute snail in a marshy source area in Bhutan, in the district Thimphu, W of Geneykha at 2825 m altitude. The locality could not yet be visited again. The specimen got lost after being photographed with a Ricoh WG-4 digital camera, using the extreme macro facility. Some equally small snails were found by Jigme Wangchuk of the Ugyen Wangchuck Institute for Conservation and Environment, Bumthang, in a source in the district Wangdue Phodrang at 2883 m altitude, and preserved in alcohol 70%. One specimen ( Fig. 1) of the latter sample, a paratype, was photographed with a digital microscope system (KEYENCE VHX-2000; KEYENCE Corp., Itasca, IL, USA) and then used for a molecular analysis. Another shell, the holotype (Fig. 2), was photographed with a Canon EOS 7D, using a Canon extension tube EF25 and a Sigma DC 18-50 mm lens.

Results
Our molecular analysis resulted in a tree ( Fig. 4) with Erhaia wangchuki sp. n. as the sister taxon of an undescribed Erhaia sp. from China, Guangxi, Xiangjiang river at Quanzhou (after Liu et al., 2014: 22). The sister taxon of these two species is unclear, but a clade formed by four species, viz. E. wangchuki, E. spec., Akiyoshia kobayashii Kuroda & Habe, 1958 and E. jianouensis (Liu & Zhang, 1979), is highly supported. Shell. Conical, broader than high, with a flat apex because the initial ¾-1 whorl is planispiral; 3¼ whorls in total. Body whorl large, the height of the aperture exceeds that of the spire. Aperture with a broadly rounded outer lip and a nearly straight parietal side, so that a columellar border is hardly recognizable. Growthlines moderately strong, with a more prominent periostracal ridge at more or less regular distances. Teleoconch whorls broadly shouldered and separated by a deeply incised suture. Aperture oblique ovoid, smooth inside; apertural edge not touching the penultimate whorl. Umbilicus widely open. The holotype is the largest shell and measures 2.15×1.77 mm.

Systematics
The shell differs from the shells of the three 'Erhaia' species reported from Nepal by Nesemann et al. (2007) by the large body whorl, the relative height of the aperture, and by being broader than high. The other species that are referred to as Erhaia in the literature, from areas that are further apart than Bhutan and Nepal, also have different combinations of character states.
Notes. This species is known from the source of the Gangzetem brooklet, emerging from an underground spring aquifer surrounded by blue pine (Pinus wallichina) and a small open meadow (Figs 5, 6). The stream bed substrate, viz. pebbles, small rocks and parts of plants, is covered with dark-green algae, housing an abundant diversity of aquatic invertebrates. Alongside the brooklet are rhododendrons (Rhododendron thomsonii, R. arboretum, R. kesangae), berries (Berberies asiatica, Rosa sericea), betula  (Betula utilis), larch (Larix griffithii), daphne (Daphne bholua) and remnants of dead dwarf bamboo (Yushania microphyllus).
A farm road to the villages of Gangphel and Zizi crosses over the stream. The source is very close (~50m) to that road. The stream also spins a chhukhor, i.e. a water powered prayer wheel. At the very outlet of the stream is a water tank, which supplies drinking water to Damchu Lhakhang. The brooklet meanders into the Phobji main stream, and measures about 1100 meters. During the pre-monsoon (21.03.2015) and post-monsoon (29.11.2015), physiochemical properties of the stream were measured. The water is almost neutral (pH 7.06, 7.58) and has a nearly stable temperature (6.76, 6.20 º C).

Discussion
After its introduction by Davis et al. (1985), the classification of the genus Erhaia remained uncertain for some time. Wilke et al. (2000)  Erhaia is known by several species in China, from the Yangtze River drainage and, by one species, from the Mekong River drainage Kang 1995, Davis andRao 1997). The probability that Erhaia is represented in Nepal indeed (Nesemann et al. 2007) is considerably enhanced by the anatomically confirmed occurrence of E. nainitalensis Davis & Rao, 1997, in Nainital in northern India west of Nepal, and E. wangchuki sp. n. in Bhutan east of Nepal. It may be hypothesized that there is a radiation in Erhaia along the southern border of the Himalaya, far west and northwest of its large range in China. With hardly any spring area in Bhutan searched for micro-snails, additional species may wait for discovery there at least.