THE FRESHWATER SNAILS OF THE GENUS BYTHINELLA MOQUIN-TANDON (GASTROPODA: RISSOOIDEA: HYDROBIIDAE) FROM MONTENEGRO

New records of freshwater snails of the genus Bythinella Moquin-Tandon from Montenegro are presented. Bythinella dispersa, 1973 and B. luteola Radoman, 1976 are recognized and defined as separate species; B. taraensis n. sp., which lives partially sympatric with B. dispersa in the canyon of the River Tara, is described as new. All Bythinella spp. in Montengro inhabit the Dinaric part of the Black Sea drainage area, while it is practically absent from the Adriatic drainage area.


INTRODUCTION
The freshwater snails of the genus Bythinella are widely distributed throughout southern, central and eastern Europe and western Asia, from the uplands of Germany (Boeters, 1981) and Poland (Falniowski, 1987) in the north, to the Mediterranean and Northern Africa (Algeria; Kristensen, 1985) in the south, and from the Iberian Peninsula in the southwest to the Ukraine in the east (Son, 2006) and Turkey in the southeast (Yıldırım, 2006).Species of the genus Bythinella occur predominantly in springs and spring-fed brooks, but can be found in crevices (Boeters, 1998), or, exceptionally, in caves (Locard, 1902).Most of the members of the genus are stenothermal species which prefer temperatures of 6-10°C.The genus Bythinella is welldefined by a cylindrical shell and a penis that bears a penial appendix with a flagellum.However, the species determination in the genus Bythinella is problematic.For example, species which are anatomically distinct (e.g., B. robiciana (Clessin, 1890) vs. B. opaca (Gallenstein, 1848) cannot be distinguished genetically (Haase et al., 2007).On the other hand, species that differ only by the marginal teeth of the radula (e.g., B. angelitae Haase, Wilke & Mildner, 2007 vs. B. opaca) can be distinguished by sequencing CO1 fragments (Haase et. al. 2007).
The aim of this paper is to give an review of the Bythinella spp. in Montenegro, and to describe the new species B. taraensis n. sp.

MATERIAL AND METHODS
In 2005-2008 the junior author collected freshwater molluscs in Montenegro (see Fig. 1 for sampling localities).The snails were collected by hand-netting, 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 made with a digital camera system (Leica R8).The holotype and the paratypes are deposited in the Zoological Museum of Hamburg (ZMH).In terminology of penis morphology we follow Ponder (2003) but use for simplification the name "penial appendix" instead of his "an accessory lobe with a sucker (as an attach organ) on its distal end".

Description
The 4.5 whorls of the conically oval shell are slightly convex with a deep suture.The shells are grey and opaque, with a glossy and smooth surface.The umbilicus is closed to a slit.The apex is broad and obtuse.The aperture is oval, slightly angled at the top, with a thickened periostome, especially at the columella.The shell is 2.7-2.8mm high and 1.6-1.7  mm broad.The ratio of shell height to aperture height is 1.7-2.1.

Anatomy
The penis is about 3/4 of the length of the penial appendix.The flagellum is thin at the distal end and broad at the proximal end.The renal oviduct possesses one coil.The apex is broad and obtuse.The aperture is oval in shape.The shell is 2.8-3.0 mm high and 1.4-1.5 mm broad.The ratio of shell height to aperture height is 2.3-2.5.

Anatomy
The penis is very short, about a quarter of the penial appendix.The flagellum is long and medium in width.Remark Radoman (1983)

Locus typicus
Canyon of the River Tara, Ljevok stream.

Etymology
The species is named after the River Tara where this species was collected.

Description
The 4-4.5 whorls of the conically cylindrical shell are slightly convex with a clear to deep suture.The shells are horn-colored to grey with a glossy and smooth surface.The umbilicus is closed to a slit.
The apex is small but broad and obtuse.The aperture is oval, slightly angled at the top, with a thickened periostome at the columella.The shell is 2.5-2.7 mm high and 1.8-1.9mm broad.The ratio of shell height to aperture height is 2.1-2.2.

Animal
The mantle is pigmented in black.

Anatomy
The penis is about 1/3 shorter than the penial appendix.The flagellum is long and thin.The renal oviduct is coiled twice (Fig. 5.2).

Remarks
The new Bythinella species can be distinguished from the other two closely related Bythinella species known from the same region, B. dispersa Radoman and B. luteola Radoman, by its shell's shape and anatomy (see Table 1 for the distinguishing features).

Distribution
Montenegro; known only from the two localities in the Tara river canyon.

DISCUSSION
In Montenegro, the members of the genus Bythinella are practically absent from the Adriatic drainage area, and are limited in their distribution to the Dinaric part of the Black Sea drainage area (with the exception of one locality in the upper part of River Morača, close to the watershed of the two sea drainage areas).The reason for this was perhaps that the direction of Dinarides in its central part prevented the spread of ancestral populations from the west into the Adriatic area of the central and most of the eastern Dinarides (Radoman 1985).The species of the genus Bythinella in Montenegro mostly inhabit cold (stenothermic) karstic springs and the uppermost courses of small streams where they can form large populations.
The distribution pattern of the three species in Montenegro show that they live sympatrically in the valleys of the rivers Tara and Lim.It is not unusual that more than one Bythinella sp.occurs in the same region (eg., Bythinella magna Radoman, 1976 andB. kapelana Radoman, 1976 in close springs in Gacko Polje, Bosnia and Hercegovina -see: Radoman, 1983), and in some cases two Bythinella spp.can even be found in the same spring (Boeters & Falkner 2008).
During the last Ice Age the region of the Bythinella spp. of Montenegro was glaciated (Huges et al., 2006) so these species have been introduced post-glacially, and it would be interesting from where these species originate.The interesting questions that arise regarding the genetic isolation and origin of these species will ultimately require the application of molecular methods.The Balkan Peninsula undoubtedly was an important refugium for malacofauna during the Pleistocene Ice Ages.
Glöer & Pešić, 2006)uteola as a subspecies ofB.opaca (Gallenstein, 1848) (syn.B.  schmidti).Bythinella luteola can be easily distinguished from the latter species by its penis morphology (the penis is very short, with a flagelum which is long and medium in width in B. luteola -Glöer & Pešić, 2006).There is no reason to support the assignment of this taxon as a subspecies of B. opaca.