Corresponding author: Edmund Gittenberger (
Academic editor: Thierry Backeljau
Shells of the
Gittenberger E, Leda P, Wangchuk J, Gyeltshen C, Stelbrink B (2020) The genera
The rissooidean gastropods that are widespread over the globe have a confusing history of taxonomic rearrangements that follow the increasing amount of morphological and molecular data, the ongoing methodological refinements in cladistics and the wealth of more or less conflicting speculations in the phylogeography of the taxa. The species of the
These species are characterized by minute shells that cannot always be recognized easily from descriptions and identified because of the limited number of diagnostic characters and the fact that many conchological character states that are used in the literature cannot be strictly quantified. The general shape of the shell and the form of the aperture may be described as ovoid, conical, subcylindrical, squat, or with another term of that kind. The convexity of the whorls and the depth of the suture are equally difficult to describe unequivocally. The surface of the shells is often heavily encrusted, so that the microsculpture of the proto- and teleoconch cannot always be recognized. Despite all this, an attempt is made here to characterize the genus conchologically.
The anatomy of these micro-snails cannot easily be investigated, so that DNA sequencing has become a promising tool to investigate the systematics of the
Four species of minute snails were collected in spring areas and in a brooklet in Bhutan (Fig.
Records of the sympatric
Photographs of the holotypes of the three
The standard CTAB protocol for molluscs was used for the DNA lab isolation (
The following abbreviations are used: B = shell breadth; H = shell height; NBCB = National Biodiversity Centre, Serbithang, Thimphu, Bhutan; NHMW = Naturhistorisches Museum, Wien, Austria.
1 | Aperture ovoid; palatal side curved and gradually passing into the basal side |
|
– | Aperture triangular with broadly rounded edges; palatal side straight |
|
The shells vary from conical to more or less ovoid, rarely with a flaring final part of the body whorl. The apex is flattened as in the European amnicolid genus Bythinella Moquin-Tandon, 1856, because of the very low spiral of the protoconch. The peristome is continuous and may be more or less protruding. The parietal and the columellar side of the aperture are about equally long and the regularly curved palatal side of the aperture gradually passes into the basal side, forming a single, regularly curved border. Bythinella cannot be distinguished from
The genus
1 | Final half of the body whorl conspicuously flaring; whorls of the spire flattened | |
– | Final half of the body whorl not flaring; whorls convex |
|
2 | Aperture measuring half the total shell height or more |
|
– | Aperture measuring less than half the total shell height |
|
3 | Shell conical, umbilical chink wide |
|
– | Shell ovoid, umbilical chink narrow |
|
4 | Parietal border of the aperture attached to the body whorl |
|
– | Parietal border of the aperture touching the body whorl or free |
|
5 | Spire turreted; shell base straight in side view |
|
– | Spire ovoid; peristome widened basally and shell base concave in side view |
|
Shell large for the genus (H > 2mm), ovoid, with a relatively large aperture.
Shell obliquely ovoid, with 3½-4 convex, shouldered whorls that are separated by a deep suture; clearly higher than broad; yellowish brown with fine irregular growth lines and some blackish brown periostracal ridges, one of which runs from the apertural columellar border into the umbilicus. Peristome not reflected. Parietal, columellar and a short part of the adjoining basal apertural border thickened by a whitish callus. Most specimens with a continuous peristome and a narrow umbilical chink. Protoconch encrusted in all specimens; teleoconch without spiral sculpture.
(
(Fig.
(Fig.
This species was discovered in 2012, but since only a single shell was collected then, a description was considered premature.
The epithet
Type locality of both
Shell with a partly reflected peristome, teleoconch with spiral lirae.
Shell elongated ovoid, with 3½ convex, shouldered whorls that are separated by a deep suture; clearly higher than broad; light yellowish brown with fine growth lines and some brown periostracal ridges. Peristome reflected at the columellar and the basal side. Parietal and columellar side of the aperture thickened by a whitish callus. An irregular umbilical chink only in the paratype might be represent a malformation resulting from repair of the shell wall. Protoconch encrustated; teleoconch with fine spiral lines.
(
(Fig.
The differences between the sympatric
The epithet
Shell conical, with 3–3½ convex, broadly shouldered whorls, that are separated by a deep suture; a little higher than broad; pale yellowish grey with fine irregular growth lines and some dark brown periostracal ridges, one of which sometimes running from a slightly angled site of the apertural columellar border into the umbilicus. Peristome not reflected. Parietal, columellar and about half the adjoining basal apertural border strongly thickened by a whitish callus. Most specimens with a continuous peristome and a broad umbilical chink. Protoconch with faint spiral lirae; teleoconch without spiral sculpture.
(
(Fig.
(Fig.
Only three relatively large shells form the type series of this species. Many more specimens, none of which exceed 1.7 mm in breadth and over 2.0 mm in height, were collected recently. This necessitated some adaptations in the description of the shells. Contrary to the original description, the shell should be described as higher than broad.
In their monograph on the aquatic molluscs of the Ganga River system
Type locality of
According to
(photo only).
A flaring final half of the body whorl, though not as extreme as in the holotype of
The shells are described by Nesemann and Sharma (2007: 64) as 1.6–2.0 mm high, with 4–4½ “convex” whorls, an aperture that is “ovate but not widened and not enlarged”, with an inner lip that is “thin and fused to the body whorl”; it can be distinguished from the other Nepalese
(photo only).
Nesemann and S. Sharma are mentioned as authors for this species, without specifying for what part of the text in
According to
Habitat of
(photos only). Holotype and 4 paratypes of
According to
Judging the nominal taxa on the basis of photographs of shells and additional data in the literature, we conclude that in general shape and apertural characters, i.e. a narrow umbilical chink, a virtually smooth columella, and a thickened outer and inner lip, the holotype of
Bhutan • District Lhuentse: Khardungchhu;
District Lhuentse: Jarkangchhu;
District Lhuentse: Songkhangchhu;
District Lhuentse: Fawan;
District Mongar: Chhuburee;
District Mongar: Rekpalung;
District Trongsa: Chendebji;
District Wangdue Phodrang: 40 km SSE of Wangdue Phodrang;
District Zhemgang, Kekhar,
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.
According to
The shells that are known from Bhutan (
(Fig.
This species was found in Bhutan without accompanying
The shells from Mongar, Chhuburee, and from Lhuentse, Jarkangchhu, are all decollate (Fig.
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.
The genetic distances between
The species was identified conchologically by using the data provided by
Some species of
See
Habitat of
Habitat of
Maximum likelihood tree reconstructed with RAxML BlackBox (
We would like to thank Dr Tashi Y. Dorji, Program Director of the NBC and Ms Sangay Dema (NBC) for their support and guidance to carry out this research. We also thank Mr J. Goud (Naturalis, Leiden), who made the photographs for Figures