The Bythinella spp. of Greece (Gastropoda: Hydrobioidea: Bythinelliidae)

In this article the type localities of 21 Bythinella spp. hitherto known from Greece are presented on a map. Twelve of these species are described as new for science. Unfortunately we had not enough materials for dissections, so the descriptions are based on the shell characters only, like almost all other known Bythinella spp. from Greece.


Introduction
When Schütt (1980) studied the Bythinella spp. from Greece, he could only list B. charpentieri (Roth, 1855) from the mainland, and described B. kosensis and B. cretensis from the islands of Kos and Crete. In 1988 Reischütz described B. charpentieri cabirius from the island of Samothraki by the shells of which Glöer & Georgiev 2012 could add the anatomy. In 2008 Reischütz et al. described B. beckmanni and B. atypicos, both from Peloponnese. Molecular genetic studies by Falniowski & Szarowska (2011) revealed ten Bythinella clades from continental Greece. Unfortunately the authors only worked with clades and did not deal with species names. In 2016 Falniowski & al. described B. walensae from the island of Naxos and  could describe two more species: B. rethymnonensis and B. sitiensis from the island of Crete. B. rethymnonensis was originally described as B. magdalenae (homonym, preoccupied by Yildirim et al. 2012) and got the replacement name B. rethymnonensis Glöer & Hirschfelder 2020. Analyses of Bythinella spp. revealed several cases where conclusions from morphological and sequence data would be inconsistent or even contradictory (Haase et al. 2007).
Recent investigations showed that the diversity in Bythinella is much larger than hitherto believed, thus this article is intended to present all the known Bythinella from Greece and to describe 12 new species which were found between 2009 and 2020.

Material and methods
The snails have been collected by Robert Reuselaars and fixed in 80% ethanol. The specimen were taken by hand or with a tweezers. In most cases only a few specimen were collected to avoid disturbing the small populations too much. Of the 12 new species, 7 are living in a habitat of less than 1 m 2 and in low densities (see figures 4, 5, 8, 13 and 14). In 2 cases even less than 0,25 m 2 (see figures 10 and 12).
The measurements of the shells were carried out using a stereo microscope (ZEISS) with an eyepiece micrometer; the photographs were made with a digital camera system (Leica R8). The type material is stored in RMNH (Rijskmuseum van Natuurlijke Historie Naturalis Leiden, The Netherlands) and in the collection of Robert Reuselaars.

Study Area
Greece is a hotspot for land and freshwater molluscs. Despite the fact that Greece is visited by many malacologists in the past, there is a continuous flow of new discoveries. In this article we present our findings on the freshwater genus Bythinella. As shown on the map, the destribution of this genus is almost horseshoe shaped, starting on the western side of continental Greece in Epirus, down to the Peleponnese, Crete and then moving upwards along the Turkish coast on the islands of Kos, Samos, Lesvos and Thassos with a few dispersed localities near Athens and on the islands of Naxos and Evia. It seems to be absent in the eastern continental part, roughly between Thessaloniki and Lamia. On many visits in this area in the past 20 years, no Bythinella sps were discovered. In the northern continental part of Greece, roughly below Bulgaria and FYROM, Bythinella sps. seems to be replaced by Grossuana. Species of this genus are known from FYROM and Bulgaria, but in 2018 four species were discovered in this region, three of which were new species (Glöer, Reuselaars & Papavasileiou).

Results
In Greece Bythinella spp. were assumed to local endemics and species of populations which occur at nearby locations are very different in shell shape (e.g. nos. 3-6). However, Glöer & Hirschfelder 2019 could show that 3 distinct species occur endemically on the island of Crete. We conclude with our present study that there is more diversity of species within this genus than formerly known. We present an identification key (Table 2) on the 21 known species. Although most species are only known from the type locality, we cannot exclude that there might be new discoveries of new or the here presented species in nearby localities and this identification key will be helpful in further studies on this genus.
Family Bythinellidae Locard, 1893 Genus Bythinella Moquin-Tandon, 1856 Type species by designation: Bulimus viridis Poiret, 1801 Differentiating characters: Because the Bythinella spp. in Greece are locally or regional endemic we compare the species only with those wich live in the same region each. For species delimitation see also the identification key at the end ( Habitat: strong running spring, the specimen were sparsly found on the small stones (1 per 5-6 stones) beneath the outflow of the spring. This species occupies an area of only 1 m 2 .
Etymology: Named after Kyriakos Papavasileiou who accompanied Robert Reuselaars at several trips in Greece and as to thank him for his help and support.
Description: The shell is ovate with 4-4.5 slightly convex whorls which are separated by a deep suture. The aperture is broad ovate to circular, angled at the top. The peristome is slightly reflexed at the columella. The umbilicus is closed. The body whorl takes 0.7 of shell height. The aperture is 0.8 mm high and 0.8 mm broad. The ratio of shell height to shell width is 1.6. The shell is 2.2-2.3 mm high and 1.4-1.5 mm broad.
Differentiating characters: The aperture is more circular than in B. gregoi, the umbilicus is closed and not slit-like.
Distribution: only known from type locality.  Habitat: Slow running spring, the specimen were collected from old leaves. Etymology: Named after Jozef Grego who did so much for our knowledge of the hydrobiids from the Balkan.
Description: The shell is slim ovate with 4-4.5 slightly convex whorls which are separated by a clear suture. The aperture is ovate, slightly angled at the top. The peristome is broadened at the columella. The umbilicus is slit-like. The aperture is 0.8 mm high and 0.7 mm broad. The ratio of shell height to shell width is 1.7. The shell is 2.4-2.7 mm high and 1.4-1.5 mm broad.
Differentiating characters: See Bythinella kyriaki n. sp. Distribution: Only known from type locality.
Habitat: In the concrete canal and on old leaves of the artificial basin. This species occupies an area of less than 0,5 m 2 .
Etymology: Named after Vladimir Pešić who did so much for our knowledge of the freshwater molluscs from the Balkans.
Description: The shell is ovate with 4-4.5 convex whorls which are separated by a deep suture. The aperture is ovate. The peristome is somewhat broadened at the columella. The umbilicus is closed. The body whorl takes 0.75 of shell height. The aperture is 0.9 mm high and 0.8 mm broad. The ratio of shell height to shell width is 1.6. The shell is 2.3-2.8 mm high and 1.5-1.7 mm broad.
Differentiating characters: The shell is smaller than B. klimaensis n. sp. and B. righaensis n. sp., but larger than B. radomani n. sp. In B. klimaensis n. sp. and in B. radomani n. sp. the aperture is angled at the top. In B. righaensis n. sp. the whorls of the spire are more convex than in B. pesici n. sp.
Distribution: Only known from type locality. Habitat: Artificial canal below outflow of the spring, the specimens were collected from small stones and old leaves.
Etymology: Named after Klima town.

Description:
The shell is elongated ovate with 4.5-5 slightly convex whorls which are separated by a deep suture. The apex is oblique. The aperture is ovate, slightly angled at the top. The peristome is broadened at the columella. The umbilicus is closed. The body whorl takes 0.7 of shell height. The aperture is 1.0 mm high and 0.9 mm broad. The ratio of shell height to shell width is 1.9. The shell is 2.6-3.4 mm high and 1.7-1.9 mm broad. Habitat: On small stones of the bottom of the springbasin. This species occupies an area of about 2 m2.
Etymology: Named after Righani town. Description: The shell is elongated ovate with 4.5-5 convex whorls which are separated by a deep suture. The aperture is ovate. The peristome is somewhat broadened at the columella. The umbilicus is closed. The body whorl takes 0.7 of shell height. The body whorl takes 0.7 of shell height. The aperture is 1.0 mm high and 0.8 mm broad. The ratio of shell height to shell width is 1.6. The shell is 3.1 mm high and 1.8 mm broad.
Differentiating characters: See B. pesici n. sp. Distribution: Only known from type locality. Habitat: On smal stones and old leaves in small canal below the spring. This species occupies an area of about 1 m 2 .

Bythinella radomani
Etymology: Named after Pavle Radoman to honour his work on hydrobiid snails of the Balkans. Description: The shell is slim ovate with 4.5-5 convex whorls which are separated by a deep suture. The aperture is ovate, slightly angled at the top. The peristome is broadened at the columella. The umbilicus is closed. The body whorl takes 0.7 of shell height. The aperture is 0.9 mm high and 0.7 mm broad. The ratio of shell height to shell width is 1.8. The shell is 2.5-2.8 mm high and 1.5-1.7 mm broad.

Conservation
Our contribution to the knowledge on the freshwater springsnails from Greece is important if we want to protect these species. Due to the human impact, most species in Greece are serious under stress. Most springs are used for drinking water or irrigation, see the examples in the figures 6, 7, 10, 12, 13 and 14. Another example: a short visit at the spring above Eftalopos 38° 35' 34.91509'' N 22° 30' 13.77271'' E (figure 15), after visiting the area around Nafpaktos and on the way to Athens in 2019, the type loacility of Daphniola eptalophos, showed a similar picture. This species lives in a small artificial basin of less than 0,25 m 2 . It is also serious under stress by pollution of the tobacco from cigarettes which were thrown in the small basin.
Subsequently it seems that this spring is also drying out slowly. During the visit only two alive specimen were observed. Of the Bythinella sps which are described in this article, we consider the species kyriaki, pesici, radomani, righaensis, petrosensis, olymbosensis, liandianensis and dimitrosensis as critically endangered due to a single spring, tiny area where they live in and low numbers of specimen. The others are considered as endangered because they only live in one spring with a higher number of specimen and less chance of human disturbance.