CONTRIBUTION TO THE MORPHOLOGY OF THE BULGARIAN STYGOBIONT TRUNCATELLOIDEA (CAENOGASTROPODA)

a bstract : The paper deals with morphology of the representatives of an entirely stygobiont, molecularly distinct and ancient clade of Bulgarian Truncatelloidea. Ten nominal species of seven genera (two of them new: Devetakiola Georgiev and Stoyanovia Georgiev) are analysed; six of them (except four Pontobelgrandiella species) are re-described. The knowledge of subterranean stygobiont gastropods is still limited; cave-dwelling species are mostly known only from empty shells found on the surface. The study includes all the Bulgarian stygobiont truncatelloideans known not only from empty shells. Their shells, soft part pigmentation, female reproductive organs and penes are presented. The results are compared with fragmentary data from the literature.


INTRODUCTION
The knowledge of subterranean, stygobiont gastropods is still limited. Especially cave-dwelling species are usually known only from empty shells found on the surface. Many species and genera of subterranean truncatelloideans have recently been described from Bulgaria, as a result of the regular exploration of the cave fauna (beron 2007). raDoman (1978) described the genus Pontobelgrandiella, designating P. nitida (Angelov, 1972) as the type species; its shell, soft part morphology and anatomy were described by raDoman (1983) and szarowska (2006). Later, several nominal species of Pontobelgrandiella (often as Belgrandiella Wagner, 1927) were described from Bulgaria (GeorGiev 2011a, 2013, based exclusively on the shell and penial morphology. This study deals with ten species of seven genera (Pontobelgrandiella has been presented elsewhere: rysiewska et al. 2016); the paper deals with all the nominal taxa of stygobiont gastropods known from Bulgaria and available not only as empty shells. Many of these taxa are known from one site each: Balkanica yankovi Georgiev, 2011, Balkanospeum schniebsae (Georgiev, 2011), Devetakia krushunica Georgiev et Glöer, 2011 and Devetakia mandrica Georgiev, 2012(GeorGiev 2011b, GeorGiev & Glöer 2011, GeorGiev 2012. Some are known from two sites: "Bythiospeum" stoyanovi Georgiev, 2013, "Bythiospeum" devetakium Georgiev et Glöer, 2013and Cavernisa zaschevi (Angelov, 1959 , 1913, or Iglica Wagner, 1927, are erroneously assigned to Bythiospeum (e.g. slapnik 1995. Moreover, nearly any truncatelloid with a tiny, turriform shell, found in a spring or cave, may be described as "Bythiospeum", despite the fact that it definitely does not belong to the family Moitessieriidae, and represents Hydrobiidae/Sadlerianinae (e.g. falniowski et al. 2014). The small number of specimens available -some nominal species represented by single empty shells -coupled with the rudimentary knowledge of their anatomy, biology, distribution, etc., resulted in dozens of nominal species, whose distinctness and phylogenetic relationships are doubtful.
Our molecular study of the obligatory stygobiont Bulgarian truncatelloids revealed a monophyletic, highly supported lineage, including five distinct clades of presumably generic level (osikowski et al. in press). The stygobiont snails live in populations composed of extremely small number of specimens, and are not easy to collect. Thus many species are known as empty shells only, or a few fixed specimens. The aim of this paper is to re-describe the truncatelloidean taxa inhabiting caves of Bulgaria.

SAMPLE COLLECTION AND FIXATION
Snails were collected from 13 cave localities in Bulgaria either by hand or with a sieve (Fig. 1, Table  1). The snails were washed in 80% ethanol and left to stand in it for about 12 hours. The ethanol was then changed twice during 24 hours.

MORPHOLOGICAL TECHNIQUES
The shells were cleaned with an ultrasonic cleaner, and photographed with a CANON EOS 50D digital camera. The snails were dissected and their penes photographed under a NIKON SMZ18 stereoscopic microscope with dark field and phase contrast, and a CANON EOS 50D digital camera. The female reproductive organs were drawn with a NIKON drawing apparatus. Original descriptions were used for comparisons (raDoman 1983, GeorGiev 2011b, 2012, 2013, GeorGiev & Glöer 2011, 2013

Balkanica Georgiev, 2011
Balkanica yankovi Georgiev, 2011 Material: Sulari and Yantra villages, Izvora (Padaloto, Yantra) cave, Stara Planina Mts (locality 1). Shell (Figs 2-8) very small (1.3 mm high), broad and ovate-conical with a moderately high spire formed by 3.5 relatively fast growing whorls separated by a moderately deep suture. Aperture oval to pyriform, surrounded by a well-marked continuous lip (Fig. 2). Shell yellowish and translucent. Soft parts unpigmented (Fig. 2), eyes absent. Female reproductive organs (Fig. 9), unknown until now, include a short and broad pallial accessory gland complex, a large bursa copulatrix with a moderately long duct, a broad loop of oviduct and one receptaculum seminis, small and cylindrical in shape, in the position of rs 1 (after raDoman 1973(after raDoman , 1983(after raDoman , szarowska 2006. Penis (Figs 10-12) simple, bent at half its length, and gradually narrowing, with a glandular outgrowth on its left side, at approximately half penis length.

Devetakia Georgiev et Glöer, 2011
GeorGiev & Glöer (2011)  et Glöer, 2011 from Devetashka cave (locality 6). It should be noted that GeorGiev (2011c) described, also from Devetashka cave, Belgrandiella pandurskii Georgiev, 2011, which actually represents the genus Pontobelgrandiella and should not be confused with Devetakia pandurskii. The shells of the two nominal species of Devetakia were practically identical. All the descriptions were based on the shells alone, thus the species distinctness of these taxa resulted mainly from a belief that cave fauna must be isolated and inevitably speciates without any stasis. Later, GeorGiev (2012) described a third nominal species of Devetakia, D. mandrica Georgiev, 2012, from Mandrata cave. The shell of D. mandrica was different from those of its two congeners, as the latter had much deeper sutures and more convex whorls. In this paper, all the morphological data concern D. mandrica, since the material of the remaining species was not sufficient.

Devetakia mandrica Georgiev, 2012
Material: Chavdartsi village, Mandrata cave, N foothills of Stara Planina Mts (locality 3). Shell (Figs 18-24) cylindrical or nearly cylindrical, with 4-4.5 flat whorls separated by a shallow suture. Spire high, apex flat. Aperture oval, peristome continuous, umbilicus slit-like, outer lip slightly developed; shell translucent, fragile and shiny. Soft parts unpigmented (Figs 18-24), eyes absent. Female reproductive organs (Fig. 25), unknown so far, with a moderately broad pallial accessory gland complex, a small and spherical bursa copulatrix with a long duct, broad loop of oviduct and one receptaculum seminis, small and spherical in shape, in the position of rs 1 . Penis (Figs 26-27) bent, long and narrow, gradually and regularly narrowing to the tip, with an outgrowth close to the base on its left side; this outgrowth was overlooked by GeorGiev (2012). At locality 12, a few specimens were found (Figs 28-34) with very small (slightly above 1 mm) shells resembling the ones from Yamata cave (locality 13). Operculum thin and colourless, except for the orange nucleus. Soft parts unpigmented, eyes absent.  (Fig. 35) simple and bent, without any outgrowths. raDoman (1983) drew a blunt and narrow outgrowth on the left side of the penis. Female reproductive organs include a large bursa copulatrix and one receptaculum seminis, in the position of rs 1 . At locality 13, six specimens were found with barrel-shaped shells (Figs 36-39) with 4.5 convex whorls separated by a rather deep suture. Aperture oval, peristome continuous, with a slightly marked outer lip, umbilicus in the form of broad slit. Shell white, thin-walled and translucent. Soft parts unpigmented (Figs 36-39), eyes absent. Female reproductive organs resemble the ones from locality 12 and consist of one receptaculum (in the position of rs 1 ) and a large bursa copulatrix with a short duct. Penis simple, with a small outgrowth on its left side.