Two new stygobiont snail species ( Gastropoda , Hydrobiidae ) from a spring in West Bulgaria

One new species of the genus Bythiospeum and one new species of the genus Devetakia from West Bulgaria, village of Bankya, Tran town area were described and the holotypes have been depicted.


Introduction
The Bulgarian stygofauna is one on the richest in Europe (Beron et al. 2009).Till now there are more than 30 species of snails known to inhabit the underground waters of the country (Georgiev & Hubenov 2013).Most of them have been described only by the shell morphology because living specimens could not be found.Thus the assignment of the species to the genus groups can only be provisional.
In this paper we describe two new species of stygobiotic snails from the genera Bythiospeum and Devetakia found only as empty shells in spring deposits of West Bulgaria, near the Serbian border.
The genus Devetakia differs from the genus Bythiospeum by the round shape of the aperture, its simple outer lip, not so pointed shell apex and more convex whorls (Georgiev & Glöer 2011).Because the two species described here as new differ in its size and the apex we designated these species to the genus Bythiospeum and Devetakia.

Material and Methods
The shells were collected by sieving the spring deposits by sieves.The measurements were carried out by using a stereo microscope (Zeiss) and an eye-piece micrometer, the photographs were made with a Leica digital camera system.The photographs were taken with a camera system with a digital adapter.
The material is stored in the Zoological Museum of Hamburg (ZMH), Germany.Abbreviations used: H -shell height, W -shell width.Etymology: The species is named after Dilian Georgiev`s mother Julia Georgieva.

Description:
The shell is elongate-conical to almost cylindrical with 5-5.5 slightly rounded whorls that have shining surface.The apex is rounded, the umbilicus is closed.The aperture is ovoid to slightly pear-shaped with a simple lip.The operculum and the soft body are unknown.H = 1.8-2.1 mm, W = 0.9-1.1 mm.

Differentiating features:
In comparison to all known Bythiospeum species from Bulgaria (Georgiev & Glöer 2013) and Serbia (Radoman 1983), B. juliae n. sp. is unique by having very fast growing whorls of the shell.
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.

Etymology:
The species is named after Dilian Georgiev`s wife Veselina Ivanova.

Description:
The shell is very small, elongate-conical to almost cylindrical with 4 rounded whorls that have shining surface.The apex is rounded, the umbilicus is opened.The aperture is rounded to slightly ovoid with a simple lip.The operculum and the soft body are unknown.H = 1.3-1.7 mm, W = 0.7-0.8mm.Differentiating features: From all known species from the genus Devetakia, the new species by its thin apertural lip and almost cylindrical shell is most similar to D. mandrica Georgiev, 2012 from which it differs by its smaller size (H < 1.6 mm; H = 1.7-2.0mm in D. mandrica).
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.

Figure 3 .
Figure 3.The spring emerging from rock crevices along Yablanitsa River -type locality of Bythiospeum juliae n. sp. and Devetakia veselinae n. sp.(exact sampling site pointed by an arrow).

Figure 4 .
Figure 4. Position of the sampling site of the two new stygobiotic snail species described.