New and little-known freshwater Mollusks of Ukrainian Transcarpathian

One species is new for the regional fauna ( Sphaerium nucleus ), another three are rare and their range is strictly limited to a few localities ( Musculium lacustre , Bythinella sp. and Terrestribythinella baidashnikovi ). It is discovered one additional locality of alien species Sinanodonta woodiana recently introduced into the Transcarpathian. Images of the shells, comments on taxonomy, distribution and ecology of these species are provided.


Introduction
An important stage for the preparation of regional faunistic reviews is compilation and biogeographic analysis of the data on distribution of individual species. It particularly concerns to rare species or those which findings are limited by specific habitats (caves, wells, etc.).
The territory of the Ukrainian part of Transcarpathian is covered with a dense network of river systems and is exclusively rich with water bodies of different types. This area occupies the first place in Ukraine on water supplying; besides a great amount of large constant waterways, here a lot of the small rivers, springs, small creeks and peat bogs are especially in the mountainous parts of the region (Gerenchuk, 1981).
Some authors were already referred to the regional malacofauna and noted its specific character (Zdun, 1960;Makogon, 1972Makogon, , 2014Stadnichenko, 1984;Gural-Sverlova, Gural, 2009 and others). However the analysis of available published data evidences that the species composition of fresh-water molluscs here is not clarified yet.
In the present paper we provide additional data on findings of several new, rare or little-known mollusk species which existence in the Ukrainian Transcarpathian has not been reliably confirmed so far. The comments on taxonomy, general distribution and ecological remarks of these species are provided as well.
Presented data should help hereafter to estimate more definitely the biogeographic status of the Transcarpathian malacofauna and to assess correctly a conservation status of some regionally rare species inhabiting there.

Material and Methods
The majority of samples used in the present study were collected by Yurii Furyk during the fieldwork in May 2017 in different parts of the Transcarpathian Region. One additional lot collected by Elena Degtyarenko on 02 July 2017 came from a stream in neighboring mountainous area of Ivano-Frankovsk Region (Fig. 1, Table  1). Mollusks were hand-picked from the shallow zone of water-bodies mostly from stones or macrophytes and using a hydrobiological net as well as sieve at depths of 0.5-1 m. Samples were immediately fixed with 80% ethanol, after a couple of days the alcohol was replaced.
Altogether over 250 specimens from nine localities have been examined (Table 1). For species differentiation a traditional morphological analysis and measurements of the shell were used.  Since the Transcarpathian Region abounds in various types of water-bodies we only select a few typical ecotopes to characterize a diversity of environmental conditions where the mollusks studied occurred (Fig.  2).

Results and Discussion
From the faunistic point of view the most productive are samples collected in the middle part of small rivers stream. One regionally new and one rare species of the family Sphaeriidae are discovered there in the localities 2, 3, 4 and 6 ( Fig. 1, Table 1). Three others sampling points were abounding in amphibiotic gastropod species with extremely narrow range only known so far from a very few localities (7-9). One more rarely occurring bythinellid species is found in the locality 5. Exclusively in the locality 1 plenty individuals of alien Unionidae species are registered. Below we provide the appropriate comments on taxa revealed.

, B)
Distribution: We found the nonindigenous mussel S. woodiana within the Transcarpathian Region in the Uzh River near Uzhgorod city (locality 1). Earlier the species was already registered here in the Latorytsa Riverright tributary of the Tisa River (Yanovych, 2013). In the Transcarpathian it inhabits only fastflowing water while in the Danube Delta it occurs both in the current waters as well as in canals, oxbow lakes and standing or slow-flowing waters (Yurishinets & Korniushin, 2001;Pavlyuchenko et al., 2007). This is the additional Ukrainian record of the East Asian species last decades introduced to several countries of West and Central Europe, as well as to Central Asia. Within the Ukraine S. woodiana was recorded firstly in the Danube-Sasyk canal in the South-West Ukraine (Yurishinets & Korniushin, 2001) and then in the other waterbodies of the Danube Delta (Pavlyuchenko et al., 2007). In the neighbor European countries it has been registered earlier: in Hungary, Slovak Republic (Falkner et al., 2001) and Poland (Protasov et al., 1994).

Remarks:
A high ecological plasticity of S. woodiana shell characteristics is mentioned by many authors (Protasov et al., 1994;Yurishinets & Korniushin, 2001;Pavlyuchenko et al., 2007 and others). Material sampled in the Uzh River represented with only about 10 middle-aged specimens and we couldn't evaluate the limits of their shells morphological variability. Nevertheless, presence of some conchological features in the individuals studied (e.g. apical part of valves sculptured by rough corrugated wrinkles) confirms belonging of the sampled unionids in Uzhgorod to Sinanodonta (Fig. 3, A, B). In the locality 1 also numerous individuals of Unio pictorum (Linnaeus, 1758) have been revealed.

Family Sphaeriidae Deshayes, 1855
The most common sphaeriid in the Transcarpathian Region and in entirely of Ukraine is Euglesa casertana (Poli, 1791) (Makogon, 1972;Stadnichenko, 1984). It inhabits springs and mountain streams as well as artificial ponds of the trout farms, producing there the populations accounting hundreds and thousands of individuals per square meter (Makogon, 1972). In our samples E. casertana found in Stara River and in natural pool close to the Sokyrnytsya village (localities 2 and 6). According to Makogon (1972Makogon ( , 2014   Distribution: Within the Transcarpathian Region the species is registered for the first time (locality 2). In the other parts of Ukraine Sph. nucleus was mentioned also in Polesye and Forest Step Zone (Makogon, 1972;Stadnichenko, 1984). It inhabits water-bodies of the West, North and Central Europe states; the closest to Ukraine sites are known in Hungary and Slovak Republic (Falkner et al., 2001).  (Stadnichenko, 1984;Korniushin, 1996). Spring snail of the genus Bythinella is the widespread and species-rich European gastropod taxon. The distribution area of the 83 species and subspecies currently recognized ranges from western France to the Ukraine; they also occur on some Mediterranean islands and in the Asian part of Turkey (Wilke et al., 2010). The representatives of Bythinella were attributing either to the family Hydrobiidae Stimpson, 1865 or Amnicolidae Tryon, 1863 (e.g. Anistratenko & Stadnichenko, 1995;Falkner et al., 2001;Fehér et al., 2008). Analysis of the phylogenetic data in combination with morphological/anatomical evidence this group appears to be distinct from the Amnicolidae (as well as from Hydrobiidae) and thus is treating as a separate family Bythinellidae (see Wilke et al., 2013).

Genus
Two nominal species of the genus are reported in Ukraine so far: B. austriaca (Frauenfeld, 1857) and B. hungarica Hazay, 1881 (e.g. Anistratenko & Stadnichenko, 1995) though these identifications need additional confirmation. Mature individuals of Bythinella can be distinguished from conchologically similar and somewhere sympatric occurring species of the genus Terrestribythinella by approx. 1.3 time's bigger shell and comparatively higher ratio of last whorl height to entire shell height.

Family Terrestribythinellidae Sitnikova, Starobogatov et Anistratenko, 1992
This group was introduced as a family by Sitnikova et al. (1992) basing on anatomical distinction of these snails, e.g. lacking of seminal receptacle in female reproductive system. Bouchet and Rocroi (2005) affiliated this taxon with Amnicolidae Tryon, 1863. Rank, systematic position and relationship of this group still uncertain, pending re-examination with using of additional morphological and molecular data. Distribution: By now all three nominal species of Terrestribythinella are known only from Tiachiv and Irshava districts of Transcarpathian Region (Sitnikova et al., 1992;Anistratenko, 1995;Anistratenko, Stadnichenko, 1995;Gural-Sverlova, Gural, 2009). Recently we found Terrestribythinella individuals living among the litter leaves on banks of a small stream in the territory of Carpathian Biosphere Reserve Headquarters and in Kuziy ravine (localities 7 and 8), Rakhiv district, Transcarpathian. These specimens well conform to the type series of T. baidashnikovi in main diagnostic features of shell. Also we sampled this species for the first time from the eastern side of the Carpathian chain of mountainsin a stream in the vicinity of Mykulychyn village, Yaremcha district, Ivano-Frankovsk Region (locality 9).

Remarks:
In the locality 9 besides T. baidashnikovi were found terrestrial gastropods Carychium tridentatum (Risso, 1826) and Aegopinella pura (Alder, 1830 Müller, 1774). Judging from ecotopes where the snails live they are neither strictly terrestrial, nor strictly water molluscs. Occurring of Terrestribythinella snails sympatric with terrestrial gastropods on the wet litter leaves or stones reflect their putative amphibiotic ecological preferences (Sitnikova et al., 1992;Anistratenko, 1995). These amphibious creatures apparently do not require significant amounts of liquid water for their existence.

Conclusion
Presented data enrich our knowledge on the regional malacofauna. Further analysis of the species diversity in combination with geographical and ecological characteristics of the region will likely push us to consider the Transcarpathian in Ukraine as a particular region representing a separate biogeographic unit. Estimating of the rank and faunal specificity of this unit requires further investigations with intensive field work for mollusk sampling.