New Bythinella (Gastropoda, Bythinellidae) species from western Turkey

Abstract Bythinella anatolica sp. n., Bythinella istanbulensis sp. n., Bythinella magdalenae sp. n., and Bythinella wilkei sp. n. from western Turkey are described herein. Illustrations of the shell and genitalia of the newly described taxa, together with comparisons with previously known Bythinella taxa and a key to the species from western Turkey, are also provided.


Introduction
Bythinella Moquin-Tandon, 1856, the sole genus of the caenogastropod family Bythinellidae (Szarowska 2006;Wilke et al. 2013), is composed of small sized (1-3 mm) species occurring almost exclusively in springs (rarely in upper courses of nutrient poor montane streams or caves) having relatively cold waters below 10 °C (Boeters 1998). Although typically characterized by cylindrical (sometimes ovate-conic) shells with rounded apertures, congeners are difficult to discriminate owing to intraspecific variation and the morphostatic mode of divergence observed in the genus (Falniowski et al. 2012). The genitalia of these snails is characterized by a penial appendix with a flagellum in the male (Glöer and Pesic 2010), and a J-shaped cylindrical bursa copulatrix in the female (Falniowski et al. 2009b).
Bythinella contains 132 species and subspecies (Yıldırım et al. 2006;Georgiev 2009;Glöer and Georgiev 2009;Bank 2013;Georgiev and Glöer 2013;Glöer 2013;Odabaşı and Georgiev 2014;Georgiev and Glöer 2014;Glöer and Pešić 2014) and is among the most species-rich genera in the Truncatelloidea. The geographic range of the genus extends from northern Africa and the Iberian Peninsula through central Europe to the Balkan countries, Ukraine and Turkey (Kristensen 1985;Haase et al. 2007). Until recently, only a few species had been recorded in the eastern half of this range. All 21 of the species in Bulgaria and 10 of 12 species in Romania were described within the last decade (Falniowski et al. 2009 a,b;Georgiev andGlöer 2013, 2014); although only three species are known from continental Greece (Bank 2013), the actual number is estimated to be 10 based on molecular data (Falniowski and Szarowska 2011). Together with difficulties in conchological identification mentioned above, the small number of local researchers and scant material from the area have contributed to the recognition of only a few species of Bythinella in its eastern range until recently. The case in Turkey, forming the eastern limit for the genus, does not differ much in this regard. The first mention of the genus from this country was by Schütt (1965), who reported Bythinella opaca (Frauenfeld, 1857) from Belgrad Forest in Prov. Istanbul. The assignment of the species from Istanbul to B. opaca (Frauenfeld, 1857) was later refuted by Schütt (1980) and Yıldırım et al. (2006), however the taxonomic status of this snail remains uncertain. Three additional species from the Asian part of Turkey have also been described (Kebapçı and Yıldırım 2010;Odabaşı and Georgiev 2014): Bythinella turca Radoman, 1976 from Cire spring (Prov. Isparta), B. occasiuncula Boeters & Falkner, 2001 from Kırkoluk springs (Prov. İzmir), and recently described B. kazdaghensis Odabaşı & Georgiev, 2014 from Ayazma Stream (Prov. Çanakkale).
In the present study, four new Bythinella species are described from western Turkey based on field surveys between 2006 and 2013. These species are discriminated based on details of shell morphometry, head and cephalic tentacle pigmentation, penial appendix, tubular gland, female genitalia, central tooth of radula and operculum. A comparison with other species and an identification key to other congeners described from Turkey are also presented.

Material and methods
Specimens were collected by hand-netting and preserved in 75% ethanol. Dissections and measurements of the genital organs and the shells were carried out using a Olympus SZ12 stereo microscope; photographs were taken with a digital camera system. Morphological terminology largely follows Radoman (1973Radoman ( , 1976 and Hershler and Ponder (1998 Etymology. Named after Anatolia. Description. Shell thin, usually cylindrical-ovoid (SW/SH 57.19%), appearing blackish (owing to darkly pigmented animal), with slightly rough surface; apex blunt, depressed on the left side; having 3 1 / 2 -4 very tumid whorls (more convex the left side), last whorl more inflated, sutures deep. Aperture ovoid or pear shaped, height of the aperture usually greater than penultimate whorl, umbilicus relatively broad and deep, sometimes covered by the outer lip, palatal lip margin not reflected, columellar and parietal margins broadly reflected.
Head black; tentacles unpigmented. Operculum oval and with distinct growth lines. Penis unpigmented and variable in natural position among individuals (straight to bent or folded), though not in shape. Tubular gland thickened, penial appendix usually very short (varying according to the shell size of the individuals). Bursa copulatrix narrow and elongated, rs 1 large and globular in shape. Central tooth of radula with 9 pointed cusps, 1 median and 4 each on sides; lateral margin without any cusps, but undulated; basal lip roundish (Figures 1, 2).
Measurements (  Habitat. Specimens were collected from under the stones in the spring outflow down the hill. Remarks. The new species is distinguished from other Turkish species by its larger shell dimensions and ear like shell aperture. Bythinella turca Radoman 1976 is distinguished from B. anatolica sp. n. by its blunter and shorter shell (SH 2,42 ± 0,13; max. 2.81 mm). SW/SH is close to B. istanbulensis sp. n., from which it can be distinguished by its oval shell with convex whorls. Bythinella occasiuncula and B. magdalenae, the geographically most proximate congeners, have smaller shell dimensions, while B. occasiuncula can be identified by the shorter and blunter shell shape and B. magdalenae sp. n. by smoother periphery and shallow sutures.
According to our current knowledge of Peri-Aegean Bythinella species, the area of the Aegean coast of Turkey is a center of diversity for the genus. The Eastern Aegean Islands Ikaria, Kos, Lesbos, and Chios are inhabited by B. kosensis (Schütt 1980;Bank 1988), while within the provinces of Aydın, İzmir, and Manisa on adjacent Anatolian mainland there are three species (B. anatolica sp. n., B. magdalenae sp. n. and B. occasiuncula) geographically isolated from the remainder of the species recorded in Turkey (Figure 7).

Type locality.
A small spring at the entrance of Bahçeköy in Belgrad Forest, Bahçeköy, Istanbul.
Etymology. Named after the type locality. Description. Shell broad cylindrical oval, yellowish horn-colored, surface smooth and glossy covered by a thick, solid and rough encrustation due to chemical conditions of the spring water; apex blunt; 3½-4 convex whorls, rapidly and regularly increasing to form a cylindrical shape, last whorl about 2 / 3 of the shell height, sutures relatively deep; aperture pear-shaped, height nearly the same as or slightly less than the penultimate whorl, columellar margin with an distinct inner lip reaching basal and apical corners of the aperture; operculum orange, umbilicus narrow and slit-shaped (Figs. 2a, 6a). Tubular gland relatively short and thick. Pallial roof unpigmented, head having little pigmentation (Fig. 2b), rs 1 small and attached to oviduct (Fig. 2c), thus not easily discernible.
Measurements ( Differential diagnosis. This new species is distinguished from other Turkish Bythinella species by its nearly cylindrical shell with broad and blunt apex. Small and attached rs 1 , unpigmented and light coloured pallial roof are the other key characters.
Habitat. Specimens were collected from the stones in a small spring and its pond.
Remarks. Based on shell characters only, Schütt (1965) misidentified Bythinella specimens from Belgrad Forest as Bythinella opaca (Frauenfeld, 1857), a species originally described from Carniola (Slovenia) and Italy. Bythinella angelitae was introduced as a replacement name for the preoccupied name Paludinella opaca Frauenfeld, 1857, a homonym of Paludinella opaca M. von Gallenstein, 1848, by Haase et al. (2007). The two closely related species B. angelitae and B. opaca can be morphologically separated only by radular dentition, and the geographic range of Bythinella angelitae is restricted to the border areas of Austria and Slovenia (Haase et al. 2007). Although they have been recorded in previous studies (Wagner 1941;Grossu 1956;Angelov 1960Angelov , 2000, Bythinella austriaca (Frauenfeld, 1857) and Bythinella opaca (M. von Gallenstein, 1848) have not been confirmed from the eastern Balkan countries in recent studies (Falniowski et al. 2009a, b). Therefore, there is a large distribution gap between the ranges of Central European taxa and that of B. istanbulensis sp. n.
Despite the conchological similarities, the new species is anatomically distinct from the Central European species B. austriaca and B. opaca. While the lighter pallial roof colouration is also observed in Bythinella opaca (Glöer & Pešic, 2006), B. austriaca has a dark pallial roof colouration. The new species differs from both of these taxa in having a very short and broad penial appendix (cf. long trumpet-shaped penial appendix in these species).  , who contributed greatly especially to the knowledge of the Balkan Truncatelloidea.

Bythinella magdalenae
Description. Shell ovate-conical and with 3-3,5 whorls. Apex truncated. Last whorl slowly increasing and broader than previous whorls, sutures not deep and periphery nearly flat. Aperture roundish oval. Umbilicus small, hollow shaped and covered by the lip. Operculum nucleus along left margin, oval shaped and with distinct growth lines.
Head having little amount of pigmentation, rather concentrated on the tips of the tentacles and around the mouth. Tentacles slightly longer than snout. Penis unpigmented, tapering towards the tip, tip not very pointed at its distal end but club-shaped. Tubular gland externally visible, thin, elongated and convoluted. Bursa copulatrix narrow and elongated, rs 1 globular in shape. Central tooth of radula with 9 pointed cusps, 1 median and 4 each on sides; lateral margin without any cusps, but undulated. Habitat. Specimens were collected from two small, closely proximal seepage springs. Remarks. Çaycuk Spring is very close to the type locality, thus indeed B. magdalenae sp. n. can be considered a single spot endemic as in the case of other species known from Turkey. Description. Shell oval conical, light brown, but appearing blackish due to encrustation; having 3-3.5 tumid whorls; last whorl slowly increasing and broader than previous whorls, sutures deep. Apex blunt. Aperture roundish oval, last whorl strongly descending towards aperture and aperture projected forward, lip in some individuals having a small protuberance in upper palatal margin. Umbilicus small, hollow or completely covered by the lip. Operculum ovate, translucent and with distinct growth lines.

Bythinella wilkei
Head having little pigmentation, pigment rather concentrated on bases of the tentacles and around mouth. Tentacles short and broad. Unpigmented penis tapering towards the tip, tip not pointed at its distal end; tubular gland thick and with two convolutions. Bursa copulatrix narrow and elongated, rs 1 elongate. Central tooth of radula with 9 pointed cusps, 1 median and 4 each on sides; lateral margins lacking cusps, but undulated.
Measurements ( Differential diagnosis. Excluding B. anatolica sp. n. described from Manisa Province, Bythinella wilkei sp. n. has a larger shell than other Turkish congeners. The nearly circular aperture, which is strongly descending and projected forward, is also characteristic of the new species.  Habitat. The specimens were collected from the outflow of a small spring having little vegetation and a gravel substrate.
Remarks. The species is one of the two northernmost distributed congeners in Turkey. Unlike B. istanbulensis sp. n. the new species is found in higher altitudes.
Identification key to the Bythinella species from Turkey