A new Bythinella (Mollusca: Gastropoda: Rissooidea) in the Slovak Republic

The four Bythinella species so far reported from Slovakia have been compared with a recently collected unknown species, described herein as new for science. Photos of the holotype and four paratypes in addition to the male copulatory organ are provided. All Bythinella spp. from Slovakia are depicted for comparison.


Introduction
Until 1991 only Bythinella austriaca (Frauenfeld 1859) and Bythinella pannonica (Frauenfeld 1865) (as Sadleriana pannonica) had been reported from Slovakia (Lisický 1991: 225, 226). Čejka et al. (2007: 52) added B. hungarica Hazay, 1881 andB. metarubra Falniowski, 1987 to the known fauna. Horsák et al. (2013: 45) reduced the inventory by the two latter species because their taxonomic status was not fully resolved. On the other hand Bank & Neubert (2018) accepted both species in their checklist of Fauna Europaea, and both species have been accepted by WoRMS (World Register of Marine species: www.marinespecies.org). While we have a clear evidence of B. metarubra from the territory of Slovakia, the presence of B. hungarica was not clearly confirmed so far. Two more geographically close Bythinella species are reported from Bükk Mountains in Hungary: B. tornensis (Frauenfeld, 1856) and B. thermophila Glöer, Varga & Mrkvicka, 2015. Karol Brancsík (1898 reported four more Bythinella species (B. solidula, B. fuscata, B. melanostoma and B. longula), but their taxonomical status is so far not confirmed. Haase et al. (2007: 1) found cryptic Bythinella spp. because there are species which are genetically distinct (B. angelitae and B. opaca) but can morphologically only be separated by the radular marginal teeth, on the other hand there are distinct species (B. robiciana and B. opaca) which are morphologically well defined but genetically not. Thus, taxonomy in Bythinella has to be based on the integration of morphology, anatomy and genetics (Haase et al. 2007: 1).
We follow Haase et al. (2007) and state if representatives of two populations are different in shell characters or anatomical characters which are constant, they belong to different species.
The aim of this paper is to describe a new Bythinella sp. found in Kunova Teplica at the foot of Plešivecká Planina Plateau in Slovenský Kras Mountains.

Abbreviations
Description: Shell: The cylindrical shell is corneous with 4-4.5 whorls which are slightly convex with a deep suture. Anterior to the suture the whorls are somewhat flattened. The aperture is ovate, usually compressed and angled at its apical insertion. The umbilicus is slit-like to closed. The peristome is sharp, straight or slightly reflexed at the umbilicus. The shell is 2.9-3.4 mm high.
Animal: The animal is dark to light grey pigmented.

Anatomy:
The penis and the penial appendix are of the same length; the tubular gland is of medium length, regularly broad and slightly inflated at the distal end.
Differentiating characters: It can be distinguished from the other Bythinella spp. of this region by the deep suture and the angle at the top of the aperture. The tubular gland of B. austriaca is slim proximally and thicker at the distal end while in B. steffeki it is regularly stout over the full length.

Habitat:
The new species inhabits a karstic spring zone of Závodná Vyvieračka (Fig. 9), consisting of an artificial concrete channel, small travertine waterfall, short river bed with larger limestone boulders, and an artificial pond adjacent to the spring. The spring is associated with a short conglomerate cave, inhabited by Hauffenia sp., but without presence of B. steffeki n. sp. The water outlet of the spring seasonally varies from 40-200 l/s with average temperature 10.2° C, pH 7.485 and conductivity 508 μS. The single known locality is inside an engineering plant in an industrial zone. Despite the environmental care of the management, it is still threatened by handling of mineral oils and recycling of iron deposits nearby.  Operative Program -Environment. Thanks to Thomas von Rintelen and Christina Zorn who borrowed us the syntypes of B. melanostoma. We are also grateful to Harry G. Lee from Jacksonville, Florida for the English proof read of the manuscript.