Two new species of the genus Bythinella Moquin-Tandon , 1856 ( Mollusca : Gastropoda : Hydrobiidae ) from the Western Balkan Peninsula )

Two new species of the genus Bythinella Moquin-Tandon, 1856 , i.e. B. marici n. sp. from Bosnia and Hercegovina, and B. istoka n. sp. from Kosovo were described. The holotypes of both species as well as the penis morphology are depicted. In addition a list and distribution map o f the Bythinella spp. occuring in the Western Balkan Peninsula is provided.


Introduction
The genus Bythinella Moquin-Tandon, 1856 is distributed from west Europe (the Iberian Peninsula), to west Asia.The genus have at least two centers of the species richness, France with 42 known species (Bichain et al. 2007), and Bulgaria with 22 species (Georgiev and Glöer 2014).Species of the genus Bythinella occur predominantly in springs and spring-fed brooks, where they can form large populations.Passive dispersal is difficult due to its habitat preferences, thus most of the species are locally endemic, especially in mountainous regions (Glöer and Georgiev 2011).
Phylogeographic studies show that the Balkan Peninsula (along with two other peninsulas of Southern Europe-Iberian and Apennine) was a refuge of genetic diversity during the Pleistocene (Hewitt 1999).The recent phylogenentical analysis by Falniowski et al. (2012) on the Bythinella populations in the Balkans showed the presence of two large clades, although they were weakly supported.One of them comprised the Romanian and populations from the Western Balkan Peninsula (Montenegro, and one population from Western Serbia), the other one (less genetically diversified) consisted of populations from the Eastern Balkan Peninsula (Bulgarian and Greek populations, and one population from Eastern Serbia).
According to Bank (2011) ten species of the genus Bythinella occur in region of the Western Balkan (Albania and the former Yugoslavia, except Slovenia) which is under discussion here.Glöer (2008) added two Bythinella species from Serbia, B. nonveilleri Glöer, 2008 (East Serbia) and B. pesterica Glöer, 2008 (West Serbia).According to Falniowski et al. (2012) phylogeographic analysis, the latter species belong to the 'Western Balkan Clade', while B. nonvelierri belong to clade which includes populations from Greece and Bulgaria.These two large clades in the inferred phylogeny are well-defined geographically (Falniowski The karst areas in the Dinaric region of the Western Balkan Peninsula are a hotspot of freshwater biodiversity.Most of the Bythinella species listed for the Western Balkan Peninsula are local or regional endemic, and only B. opaca (M.von Gallenstein, 1848) is widely distributed.However, it is very likely that B. opaca represents a species aggregate with many populations over a wide range of countries (Feher 2010).
The aim of this paper is to give a review of the Bythinella spp. of the Western Balkan Peninsula, and to describe the new species from Bosnia and Hercegovina and Kosovo.(1976,1983), Glöer (2008), Fehér & Erőss (2009), and Glöer & Pešić (2010).

Material and Methods
The snails were collected with a sieve or by hand, sorted on the spot from living material and preserved in 75% ethanol.The dissections and measurements of the genital organs and the shells were carried out using a stereo microscope (Zeiss); the photographs were taken with a digital camera system (Leica).
The following characteristics are used in identification of Bythinella spp.: (i) the shell: shape, height, ratio of aperture height of shell height, umbilicus, aperture, and (ii) the male copulatory organ: ratio of the length of the penis to the penial appendix, flagellum length, width of the proximal and distal part of the flagellum.The shape of flagellum has been often overlooked, but this seems to be an important feature to distinguish Bythinella spp (Glöer and Georgiev 2011).The male copulatory organ was studied on at least three specimens from every sample to find the constant features of this organ.
The studied material is stored in the Zoological Museum Hamburg (ZMH) and the private collection of the senior author. .

Description
Shell.The large shell is whitish and cylindrical.The 4.5 whorls are convex with a very deep suture.The surface is silky and finely striated.The apex is obtuse, the umbilicus is slit-like.The aperture is oval.Shell height 3.3-3.5 mm, width 2.0-2.1 mm mm, height aperture/shell ratio 0.43.
Soft body.The mantle is black with a greyish boarder, the head is whitish.The penis is shorter than the penial appendix.The flagellum is long, thin at the proximal end and broad at the distal end.
Differentiating features.It is one of the largest species of this genus in the Balkan Peninsula.Only two Bythinella species from the Gacko polje, a karstic field (= polje) in Croatia, are larger: B. magna Radoman 1976, with a shell height of 4.55-5.21(Radoman 1983: 209)  Etymology.Named after the town (Istok) where the species was found.

Description
Shell: Shell whitish, cylindrical, its 4.5 whorls slightly convex, with a deep suture.The first two whorls small in height, the other whorls are fast growing.Surface silky and finely striated.Apex obtuse, umbilicus closed.Aperture oval, its top angled, periostome thickened at the columella.Shell height 2.7-2.8mm, width 1.5-1.6 mm, height aperture/shell ratio 0.46.Soft body.The mantle is black, the head is greyish with a dark stripe from eye to eye.Penis shorter than penial appendix.The flagellum is long, attenuated proximally.
Differentiating features.Bythinella istoka n. sp.can be distinguished from the other species of this genus from the Western Balkan by the first two whorls, which are small in height.The similar shape of the first two whorls is found in B. taraensis, but the shell of the latter species is broader (1.8-1.9 mm vs. 1.5-1.6 mm in Bythinella istoka n. sp.) by nearly the same shell's height.In addition B. taraensis differs by the flagellum which is longer, and thin along the entire length.
Distribution.Kosovo; known only from the type locality (Fig. 15).

Figure 1 .
Figure 1.Distribution of the species of the genus Bythinella in the Western Balkan Peninsula.Sampling sites of the new Bythinella species are marked by red dots.The distribution map is made considering the papers by Radoman(1976, 1983),Glöer (2008), Fehér & Erőss (2009), and Glöer & Pešić (2010).

Research Article et al
Radoman, 1976we can speculate that the third Serbian Bythinella species, B. serborientalisRadoman, 1976, from East Serbia, belong to the latter clade.

Table 1 .
Species of the genus Bythinella in the Western Balkan Peninsula.
Radoman 1976anaRadoman 1976with a height of 4.33-4.70.In addition to the dimensions, these species differ in the shape of aperture: in B. magna the aperture is a relatively low (height aperture/shell ratio 0.38, data taken from Radoman 1983) while in B. kapelana aperture is nearly elliptical.Bosnia and Hercegovina; known only from the type locality (Fig.14).