New taxa of subterranean freshwater snails from Bulgaria ( Gastropoda , Hydrobiidae )

Two new genera, i.e. Kolevia gen. nov. and Microstygia gen. nov., in addition to the five subterranean species were described here as new for science: Kolevia bulgarica n. gen. n. sp., Microstygia deltchevi n. gen. n. sp., Bythiospeum iltchoi n. sp., Belgrandiella lomica n. sp., and Belgrandiella delevae n. sp. The type species of the new genera are designated, holotypes of the new species are depicted, and a map with the sampling sites is provided.


Introduction
For a long time the Bulgarian stygobiotic snail fauna was poorly known (Angelov 2000).After an intensive research by authors after 2009 many new species were described from particular regions of the country as West Rhodopes Mts., Central and Western Stara Planina Mts., and its north foothills, known as "Predbalkan" (Georgiev & Hubenov 2013).However some geographical regions remained unexplored.
In this paper we describe new taxa of snails from subterranean waters of such areas (western mountainous regions near the Serbian border, Danube plain and East Stara Planina Mts.), and one from the relatively known Vrachanski Balkan Mts.(part of Western Stara Planina) (Fig. 1).Two of the new species were representatives of unknown genera described here as new.

Material and Methods
The shells were collected by sieving the spring deposits by sieves.The measurements were carried out by means of ZEISS stereo microscope and an eye-piece micrometer.The photographs were taken with a digital camera system (LEICA).
The material is stored in the Senckenberg Naturhistorische Sammlung Dresden (SNSD), Germany and in the collection of the authors.Abbreviations used: H -shell height, W -shell width.Type species: Kolevia bulgarica n. gen.n. sp.

Diagnosis:
The shell is white, conical to ovate-conical with 5 whorls having fine growth lines and deep suture.The apex is rounded to relatively sharp.The aperture is ovoid with simple lip having brownish periphery.The umbilicus is slit-like.The operculum and the soft body are unknown.

Etymology:
The genus is named after Iltcho Kolev who collected the type species.

Differentiating features:
In Graziana Radoman, 1975 the aperture is elongated ovate and not as broad as it is in Kolevia n. gen.The shells of Cavernisa Radoman, 1978

Description:
The shell is white, conical to ovate-conical with 5 whorls having fine growth lines and deep suture.The apex is rounded to relatively sharp.The aperture is ovoid with simple lip having brownish periphery.The umbilicus is slit-like.The operculum and the soft body are unknown.H = 8.9 mm, W = 2.4 mm.

Habitat and ecology: Stygobiotic species.
Distribution: Known only from its type locality.

Diagnosis:
The shell is white, elongate-conical to almost cylindrical with 4 whorls having fine growth lines and deep suture.The apex is strongly rounded.The aperture is ovoid with a simple lip having relatively thickened edge.The umbilicus is open.The operculum and the soft body are unknown.Etymology: From "micro" and "Styx River", meaning micro inhabitant of subterranean waters.

Differentiating features:
The new genus is most similar morphologically with Bythiospeum Bourguignat, 1882 and Paladilhiopsis Pavlovic, 1913.From both it differs by its rounded apex and broad embryonic whorls.In addition from the first it differs by its open umbilicus and from the second by the lack of spiral lines microsclupture on the shell crossing the growth striate.

Etymology:
The species is named after the arachnologist and speleologist Assoc.Prof. Christo Deltchev (National Natural History Museum, Sofia) for his contributions in studies of the Bulgarian caves and cave fauna.

Description:
The shell is very small, elongate-conical to almost cylindrical with 4 slightly rounded whorls that have shining surface.The apex is rounded, the umbilicus is wide open.The aperture is ovoid with a simple lip having relatively thickened edge.The operculum and the soft body are unknown.H = 1.25 mm, W = 0.6 mm.

Differentiating features:
Comparing to all known Bythiospeum species from Bulgaria (Georgiev & Glöer 2013) and Serbia (Radoman 1983), Microstygia deltchevi n. sp.differs from all by its very round apex and wide open umbilicus.In addition this species has very small shell (H < 1.3 mm).
Habitat and ecology: Stygobiotic species found only as empty shells among sand deposits of a spring emerging from rocks, at a river bank.The area was occupied by broad leaf forest dominated by Fagus sylvatica, Carpinus sp., and Alnus glutinosa.Shells were found together with those of Bythiospeum juliae Georgiev &Glöer, 2015 andDevetakia veselinae Georgiev &Glöer, 2015 (also type locality of these species).

Figure 1 .
Figure 1.Collection sites of the new hydrobiid species in Bulgaria: 1: Kalna Matnitsa spring; 2: Spring on the left bank of Yablanitsa River; 3: Water source near Beli Lom River; 4: Stream flowing from village of Golyamo Gradishte at its inflow in Kalakoch River; 5: Lednika Cave, Kotel town area.