Erhaia norbui: A new species of freshwater Snail from Bhutan.

Gastropods of the genus Erhaia are small aquatic Snails with ovoid shells less than 5 mm high, single gills and opercula, found in clear freshwater environments across a broad area of northern India, Nepal, Bhutan, and eastern China, with a total east-west distribution range of about 3500 km. These Snails are usually found in springs and brooklets, and show a high rate of endemism, with many species only known from a limited area or even single location. To date, three members of this genus have been described from Bhutan, two of which are found at single locations in Latipur and Kavre districts, with the third found at both of these locations, plus a further four localities.

In a paper published in the journal ZooKeys on 2 February 2022, Edmund Gittenberger of the Naturalis Biodiversity Center, and GiMaRIS, Choki Gyeltshen of the National Biodiversity Centre of Bhutan, and Björn Stelbrink of the Department of Animal Ecology & Systematics at Justus Liebig University Giessen, describe a new species of Erhaia from Haa District in Bhutan.

The new species is named Erhaia norbui in honour of Sangay Norbu, who discovered the population from which the species is described. The description is based upon six shells, collected from a spring at an altitude of 2700 m above sealevel, close to the village of Naychu. 

 

Erhaia norbui from the type locality, district Haa, Uesu, Naychu, roughly 2700 m above sealevel. (3) Holotype, NBCB 1239 (height 2.3 mm) and paratypes used for DNA analyses (4 UGSB 25956,height 1.5 mm 5 UGSB 25957, height 1.8 mm). Scale bar is 1 mm. Gittenberger et al. (2022).

Erhaia norbui has a ovoid to elongate ovoid or conical shell, smooth or with spiral microsculpture on the proto- and/or teleoconch (the protoconch is the embryonic shell of a Snail, which remains attached to the later shell, or teleoconch, and is often quite different in structure, making it a useful taxonomic tool). The apex of the shell is conspicuously and obliquely flattened. The aperture of the shell varies from ovoid-elliptical to circular; its palatal side is curved and gradually passes into the basal side. The peristome (layer of skin covering the shell is continuous, attached at the parietal side or slightly protruding. The umbilicus (gap inside the spirals of some Snail shells) is minute or closed. The parietal part of the aperture is smooth or with a lamella; columella smooth or with 2 spiral lamellae.

 

Habitat of Erhaia norbui at the type locality. Sangay Norbu in Gittenberger et al. (2022).

A DNA analysis based upon mitochondrial markers, plus the gened which code for the cytochrome c oxidase I protein and 16S rRNA, established that Erhaia norbui is a separate species, genetically differentiated from all other Erhaia species, but also that the three Erhaia species which are found in Bhutan and which were included in the study, form a distinct clade, all being more closely related to one another than any of them is to any species found outside the kingdom.

 

Maximum likelihood tree reconstructed with RAxML BlackBox (GTR+G substitution model for each partition and 100 bootstrap replicates), with new data in red. Numbers on branches denote bootstrap values of more than 50. Gittenberger et al. (2022).

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