Revision of the subterranean genus Spelaeodiscus Brusina, 1886 (Gastropoda, Pulmonata, Spelaeodiscidae)

Abstract The Balkan genus Spelaeodiscus Brusina, 1886 is revised based on museum collections and newly collected samples from Montenegro and Albania. The following species and subspecies are introduced as new to science: Spelaeodiscus albanicus edentatus Páll-Gergely & P. L. Reischütz, ssp. n. (southern Montenegro and northern Albania), Spelaeodiscus densecostatus Páll-Gergely & A. Reischütz, sp. n., Spelaeodiscus hunyadii Páll-Gergely & Deli, sp. n., Spelaeodiscus latecostatus Páll-Gergely & Erőss, sp. n. (all three from southern Montenegro), Spelaeodiscus unidentatus acutus Páll-Gergely & Fehér, ssp. n., and Spelaeodiscus virpazarioides Páll-Gergely & Fehér, sp. n. (both from northern Albania). For all species and subspecies diagnoses and suggestions for conservation status assessments according to IUCN criteria are provided. An overview is given regarding the habitat preference of Spelaeodiscus species, and the “scratch and flotate” method to collect subterranean gastropods.


Introduction
Spelaeodiscus was described by Brusina (1886) as a subgenus of Patula Held, 1838. At that time, the only species in this group was P. (S.) hauffeni (Schmidt, 1855). This group (and the only species belonging to it) was known to inhabit Krain (Slovenia) only. The second species of Spelaeodiscus was Spelaeodiscus albanicus (A. J. Wagner, 1914), which was described from northern Albania, based on shells collected in the debris of the Kir River. Spelaeodiscus was first used at the genus level by Pilsbry (1926). In the 1960's Bole (1961Bole ( , 1965 and Gittenberger (1969) introduced three additional species as follows: S. unidentatus Bole, 1961, S. obodensis Bole, 1965and S. dejongi Gittenberger, 1969. The former two were described from present day Montenegro, whereas S. dejongi was originally reported from Slovenia. Later it turned out that the Slovenian specimens of S. dejongi were probably the result of mislabelling, and that this species is endemic to Montenegro (Gittenberger 1975). Thus, Spelaeodiscus is currently known from the Western Balkans (Slovenia, Montenegro, and northern Albania).
Aspasita and Spelaeodiscus have been distinguished by Schileyko (1998) and Subai and Dedov (2008) on the genus, by Gittenberger (1969Gittenberger ( , 1975 on the subgenus level. However, Welter-Schultes (2012) treated them as a single genus. In this paper we treat the two genera separately.
The conchologically similar genus Virpazaria Gittenberger, 1969, which is also an endemic of the West Balkans, is distinguished from Spelaeodiscus and Aspasita on the basis of the continuous peristome and the crescent-shaped aperture (Gittenberger 1969, 1975, Reischütz and Reischütz 2009. So far, Spelaeodiscus species have mainly been reported from caves, and thus, they belong to the rarest genera in mollusc collections. Intensive field surveys in Montenegro and Albania, and using special collecting methods (sieving and flotating the granular rocky substrate collected from rock crevices) significantly increased the number of known populations and the amount of the available shell material of Spelaeodiscus. In the present revision we present the outcome of the examination of all available historical and newly collected material.

Materials and methods
The new samples were collected between 2010 and 2017 during 13 collecting trips. Sampling was done scratching out fine granulate material from the superficial fissures of rocks applying long and narrow hand rakes and separated the shells either by sieving ("scratch and sieve" method) or by flotating ("scratch and flotate" method).
Shell whorls (± 0.25) were counted according to Kerney and Cameron (1979: 13). Most shells were measured in mm to one significant digit using Zeiss Stemi 305 microscope with Zeiss Labscope software. The measured parameters are compiled on Figure 1. Ribs on the body whorl were counted using photographs of 3-5 shells per population. Differences in size are indicated in the diagnoses using the following terms: small (1.9-2.5 mm), medium sized (2.6-3.5 mm), large (3.6-4.3 mm).

Systematics
Family Spelaeodiscidae Steenberg, 1925 Remarks. Schileyko (1998) classified Spelaeodiscus into the family Spelaeodiscidae Steenberg, 1925, which has independently been introduced by Hudec (1970) as well. This taxon was also recognized as a separate family of the infraorder Orthurethra (and its only superfamily, Pupilloidea) by Bouchet et al. (2017). Although the genital anatomy of some species belonging to this family is known, its systematic position within Orthurethra is uncertain, because no molecular phylogenetic information is known (Harl et al. 2017).

Genus Spelaeodiscus Brusina, 1886
Patula (Spelaeodiscus) Brusina, 1886: 37. Type species. Helix Hauffeni Schmidt, 1855. Distribution. The genus Spelaeodiscus has a disjunct distribution. One species (S. hauffeni) is only known from Slovenia, whereas the rest of the genus is distributed in the vicinity of the Skadar Lake Basin (also known as Shkodër Lake or Skutari Lake) in Montenegro and northern Albania (Figure 2).
Delimitation of this genus. The reproductive anatomy of Spelaeodiscus and Aspasita is characterized by a short penial caecum, a well-developed penial appendix, sometimes an epiphallic caecum, and a bursa copulatrix without a diverticulum. The retractor muscle is divided into two bounds, one inserting on the penial appendix, whereas the other at the base of the penial caecum. Examining the anatomical descriptions and drawings of Spelaeodiscus (Bole 1965) and Aspasita (Hudec 1965, Gittenberger 1975, Schileyko 1998, Subai and Dedov 2008, we were unable to find characters that would constantly differ between the two groups. For example, the penial caecum was long and slender in A. tatrica (see Hudec 1965) and S. hauffeni (see Bole 1965), but was short and conical in A. triaria (see Subai and Dedov 2008) and S. unidentatus (see Bole 1965). Also, the shape of the bursa and the position of the starting point of the penial appendix was greatly variable across genera. Clear epiphallic caecum was only found in S. hauffeni, but some thickening was visible in S. unidentatus and A. triaria.
As for shell characters, Spelaeodiscus is characterized by a mostly colourless shell that is smaller than 4.3 mm (majority of species are even smaller than 3.5 mm), the spire is relatively low (height of body whorl at least two third of the height of the en-  tire shell), the body whorl is evenly rounded, the edge of the parietal callus is straight, and the peristome is only slightly expanded. In contrast, Aspasita shells are brownish, larger than 4.3 mm, they have higher spire (height of body whorl is approximately half of the height of the entire shell), the shell is shape reverse trapezoid from standard apertural view, the callus is heart-shaped, and the basal part of the peristome is strongly expanded. The habitat was the only "trait" mentioned by Gittenberger (1969) as difference between the two groups. Namely, Spelaeodiscus is subterranean, whereas Aspasita can be found on rock surfaces and among leaf litter at the base of limestone rocks. In the lack of sound molecular data it is difficult to infer their relationship, but based only on ecological, conchological, and biogeographical differences it seems reasonable to keep Aspasita and Spelaeodiscus as distinct genera.

Spelaeodiscus albanicus (A. J. Wagner, 1914)
Diagnosis. A large species with usually widely spaced, strong ribs, and no or weak apertural teeth. Differential diagnosis. The most similar species in terms of shell size and shape is Spelaeodiscus densecostatus sp. n., for differences see under that species. Spelaeodiscus unidentatus is usually smaller, usually possesses denser ribs, and has stronger teeth and narrower aperture.
Conservation status. Reischütz and Fehér (2017) assessed this species as Least Concern (LC). They claimed that there are at least three known locations and is likely that further field work reveals a larger range and more locations. Although that assessment was based partly on incorrect distribution records (Peuta Cave population is currently treated as S. unidentatus, whereas Raps-Starjë population as S. virpazarioides sp. n.), together with our new distribution records there are more than five locations. As we have no reason to suppose that the habitat quality, habitat extent, or population are deteriorating or extremely fluctuating, Least Concern (LC) seems to be a correct assessment. Figure 3 Aspasita albanica A. J. Wagner, 1914in Sturany & Wagner 1914 Fig. 3A-F); Drinasca-Ufer b. Skutari (angeschwemmt), leg. Sturany, 03.05.1905, NHMW 112351 (1 corroded, juvenile paralectotype).
Description. Shell rarely flat, usually spire somewhat elevated; protoconch consists of 1.5-1.75 whorls, very finely granulated, rather matte, not glossy; teleoconch with strong, equidistant ribs that are supported by fine periostracal filaments in fresh shells; rib density variable (43-93 ribs on body whorl), usually widely spaced; between main ribs some fine wrinkles discernible; entire shell with 4.25-4.5 whorls; aperture semilunar or due to the straight basal part triangular; peristome expanded and slightly reflected, especially on the palatal, basal and umbilical areas; palatal tooth of variable strength, usually weak, although present in all adult shells, palatal region of peristome without outer incision; basal portion of peristome usually straight, slightly thickened, with two low denticles that are visible in all adult shells; umbilicus funnel-shaped, wide (although width depends on spire height).
Variation among specimens. Some variability was found between populations in terms of rib density, spire height, and strength of apertural teeth.
Differential diagnosis. This new subspecies differs from the nominotypical subspecies in the following traits: aperture relatively larger, and its basal area not straight; apertural barriers (teeth) absent; protoconch smooth, glossy; ribs somewhat less dense (rib density on body whorl: 35-54).
Variation among specimens. This subspecies shows some variability in terms of shell size and rib density.
Etymology. This new subspecies is named after its toothless aperture, which distinguishes it from the nominotypical subspecies.
Distribution. This taxon is found in the northeastern part of the Lake Shkodër Basin ( Figure 4).
Differential diagnosis. See under S. obodensis and S. hunyadii sp. n. Variation among specimens. This is a widely distributed species with numerous known populations, most of them with unique character states of spire height, shell size, and rib density.
Distribution. This species is distributed in the Rumija Mountain between the Shkodër Lake Basin and the Adriatic Sea. Northwards the range extends to the Cetinje area. According to the original labels, type material is of Slovenian origin, however, this species was never again found in Slovenia. It can be reasonably supposed that it is due to mislabelling and the 'type locality' is not the site where the type material actually came from (Gittenberger 1975). Welter-Schultes (2012) reports the species only from Slovenia, which is based on the originally incorrect type locality.
Conservation status. Assessed as Least Concern (LC) by Reischütz (2017a), because it is not an extremely rare species and there is no reason to suppose that the habitat quality, habitat extent or population are deteriorating or extremely fluctuating. Now, the number of known locations is more than 20, which confirms the LC status. Type locality. Montenegro, Hotel/Restaurant Izvor north of Sutomore. Diagnosis. A large species with very low and dense ribs; aperture toothless. Description. Spire slightly elevated; protoconch consists of slightly more than 1.5 whorls, rather glossy; teleoconch with very fine, low, equidistant riblets (approx. 112 on the body whorl); between main ribs some fine wrinkles discernible; entire shell with 3.75 whorls; aperture semilunar, peristome; peristome expanded and slightly reflected on the basal and umbilical areas; aperture toothless; umbilicus regular funnel-shaped, relatively wide.

Spelaeodiscus densecostatus
Measurements. SW = 3.7 mm, SH = 1.8 mm, AW = 1.5 mm, AH = 1.4 mm (holotype). Differential diagnosis. Spelaeodiscus densecostatus sp. n. differs from S. albanicus by the smaller shell and the much denser and lower ribs on the teleoconch. Furthermore, S. albanicus albanicus has two basal and a palatal tooth in the aperture.
Variation among specimens. The only known adult shell is the holotype. Therefore, the morphological diversity within population is unknown.
Etymology. This new species is named for its dense ribs, which distinguishes it from the most similar S. albanicus.
Distribution. This species is known from the type locality only (Figure 7). Conservation status. The number of known locations of this species is less than five (i.e. known from a single site) and AOO is smaller than 20 km 2 , but there is no reason to suppose that AOO, EOO, number of locations, number of subpopulations or the number of mature individuals are declining or extremely fluctuating. Therefore, it should be assessed as Near Threatened (NT).  Other material. Velikajama, Soko Kod, Sela Dopilo (geographic position unknown), coll. Edlauer ex coll. Dabović, NHMW 48473/2 shells (1 adult + 1 juvenile) (in brackets: neben 49.999, probably mistyped 48.999, because this was a mixed lot of S. hauffeni and S. dejongi; this is obviously incorrect locality for this species); Jama nadjama pri Gnezdu (Izilovice) (= Jama pri Gnezdu at 45. 939°N Fig. 8F-J).

Diagnosis.
A medium sized species with very widely spaced, strong ribs, rounded, toothless aperture, and finely granular protoconch.
Description. Spire somewhat elevated; protoconch consists of 1.5-1.75 whorls, very finely granulated, rather matte, not glossy; teleoconch with strong ribs that are supported by fine periostracal filaments in fresh shells; ribbing less regular than in other congeneric species; ribs widely spaced (41-52 ribs on body whorl); between main ribs some fine wrinkles discernible; entire shell with 3.75-4.25 whorls; aperture toothless, semilunar/rounded; peristome slightly thickened, slightly reflected in direction of umbilicus; umbilicus regular funnel-shaped, relatively narrow.
Variation among specimens. Spelaeodiscus hauffeni shows some variability in terms of shell size and spire height, but the rib density and the formation of the aperture are stable characters. Distribution. This species is distributed in the southeastern Alps (Central Slovenia) relatively far from the ranges of its congeneric taxa. Slapnik (2005) found shells in the Škocjan Caves Regional Park, which are probably of Holocene age (Figure 9). Conservation status. As there are several known locations and no reason to suppose that the habitat quality, habitat extent or population are deteriorating or extremely fluctuating, it was assessed as Least Concern (LC) by Reischütz (2017b). Diagnosis. A small, nearly flat species with strong, widely spaced ribs, glossy protoconch and strongly oblique, toothless aperture.
Variation among specimens. Specimens of the type sample show no notable conchological variability. Etymology. This new species is named after our colleague and friend, András Hunyadi, who is one of those who first collected this species.
Distribution. This species is known from the type locality only (Figure 7). Conservation status. To our present knowledge this species is very rare (currently known from a single location) and thus AOO is smaller than 20 km 2 . However, there is no reason to suppose that AOO, EOO, number of locations, number of subpopulations or the number of mature individuals are declining or extremely fluctuating. Therefore, it might be assessed as Near Threatened (NT). Diagnosis. A small, nearly flat species with strong, very widely spaced ribs, glossy protoconch and a toothless aperture.
Differential diagnosis. The widely spaced ribs are similar to S. hunyadii sp. n., but the less oblique aperture distinguishes S. latecostatus sp. n. from the other new species. Spelaeodiscus dejongi, which lives sympatrically with S. latecostatus sp. n., is similar in shell shape and size and the formation of the aperture, but has much denser ribs.
Variation among specimens. See remarks.
Etymology. This new species is named after its remarkably widely spaced ribs.

Distribution. See under Remarks and Figure 7.
Remarks. The holotype of this species was found in a large sample of S. dejongi. Therefore, even if the shell shape does not differ from that species, the widely spaced ribs indicate that S. latecostatus sp. n. differs from S. dejongi on species level. Three shells from 1 km S of Seoća possess denser ribs than other S. dejongi populations (47-54 ribs on the body whorl), but obviously the rib density is lower than that of the holotype of S. latecostatus sp. n. Since the rib density of that population is intermediate between S. dejongi and S. latecostatus sp. n., it is not possible to decide which species it belongs to. More populations around the sample from 1 km S of Seoća site are necessary in order to provide a reliable identification. Here we provisionally identify those shells as Spelaeodiscus cf. latecostatus sp. n.
Conservation status. To our present knowledge this species is very rare (currently known from two locations) and thus AOO is smaller than 20 km 2 . However, there is no reason to suppose that AOO, EOO, number of locations, number of subpopulations or the number of mature individuals are declining or extremely fluctuating. Therefore, it might be assessed as Near Threatened (NT). Bole, 1965 Figures 11, 12 Spelaeodiscus obodensis Bole, 1965: 350, plate

Diagnosis.
A medium sized species with elevated spire, roughly sculptured protoconch, strong ribs on the teleoconch, and toothless aperture.
Variation among specimens. This species is the most variable in terms of shell size and rib density.
Distribution. This species is found northwest of the Shkodër Lake Basin, as well as in the Zeta River Valley between Podgorica and the Ostrog Monastery (Figure 4). The Albanian record given by Reischütz et al. (2013) and referred by Reischütz (2017c) is actually S. albanicus edentatus ssp. n. So far, no Albanian occurrence is known.
Conservation status. As there are at least seven known locations and no reason to suppose that the habitat quality, habitat extent or population are deteriorating or extremely fluctuating, it was assessed as Least Concern (LC) by Reischütz (2017c).  Bole, 1965 (A) and Spelaeodiscus unidentatus unidentatus Bole, 1961 (B). Bole, 1961 Diagnosis. A small to medium sized species with dense riblets, and strong parietal and basal teeth/thickenings. Differential diagnosis. This species differs from most other Spelaeodiscus species by the presence of two well-developed apertural teeth (a palatal and a basal). See also under Spelaeodiscus albanicus.

Spelaeodiscus unidentatus unidentatus Bole, 1961
Description. Spire elevated; protoconch consists of 1.5 whorls, roughly granulated/"hammered", matte, not glossy; teleoconch with strong but dense, equidistant ribs that are supported by fine periostracal filaments in fresh shells; rib density variable (74-118 ribs on body whorl); between main ribs some fine wrinkles discernible; entire shell with 3.75-4.5 whorls; aperture semilunar or triangular due to straight basal part; peristome thickened, slightly expanded and slightly reflected on the palatal, basal and umbilical areas; palatal tooth strong, pointed; palatal region of peristome with strong outer incision (i.e. the position of the palatal tooth is indicated with a groove on the outer side); basal portion of peristome straight, thickened; occasionally two small denticles visible, sometimes only the one situated closer to the palatal side is developed as a low denticle; umbilicus funnel-shaped, wide to relatively narrow (width depends on spire height).
Differential diagnosis. See under S. unidentatus acutus ssp. n. Variation among specimens. This subspecies is particularly variable in terms of shell size. The shape of the thickening of the basal part of the peristome is also slightly variable, although it never develops to a pointed tooth.
Distribution. This taxon is found north and northwest of the Shkodër Lake Basin in Montenegro (Figure 7). Albanian records given by Reischütz et al. (2013) actually refer to S. unidentatus acutus ssp. n.
Remarks. The only sample in the MZBI, which was collected before the original description is from Obodska pećina represent the type sample of this species (MZBI 1019). Bole collected both S. obodensis and S. unidentatus at Obodska pećina in September, 1956, but described only one (S. unidentatus) in 1961, and the other (S. obodensis) in 1965.
Differential diagnosis. Spelaeodiscus unidentatus acutus ssp. n. differs from the nominotypical subspecies by the strong, pointed basal tooth, which is blunt, or represented as a thickening of the basal peristome in the nominotypical subspecies. Moreover, the palatal region is not or only slightly "pushed" from the outside in the position of the palatal tooth. Rib density: 64-91 ribs on the body whorl.
Variation among specimens. This subspecies is variable in terms of shell size and spire height, i.e. one population has a nearly flat shell.
Etymology. This new subspecies is named after its pointed (Latin: acutus) basal tooth, which distinguishes it from the nominotypical subspecies.
Distribution. This subspecies is known from the southeastern side of the Shkodër Lake Basin in Albania (Figure 7). Type locality. Albania, Malësia district, a mountain pass 2 km N of Rraps-Starjë, 700 m a.s.l., 42°24.888'N, 19°30.240'E. Diagnosis. A medium sized to large species with elevated spire, strong, very widely spaced ribs, fine spiral lines consisting of series of minute tubercles, hammered protoconch, weak basal thickening, weak parietal tooth, and a thickened parietal callus.
Differential diagnosis. This new species can be distinguished from all congeners (especially the most similar S. albanicus albanicus) by the clearly visible spiral striation, roughly sculptured protoconch and thickened parietal callus. All Virpazaria species possess an elevated parietal callus, but it is sharp in most (all?) species, and the aperture of those species are more slender, crescent-shaped.
Variation among specimens. The degree of the thickness of the parietal callus shows some recognisable variability within the single known population, but this trait might be due to the age (degree of development) of the examined shells.
Etymology. This new species is named after its resemblance to Virpazaria species based on the thickened parietal callus.
Distribution. Spelaeodiscus virpazarioides sp. n. is known from the type locality only (see also Figure 7).
Remarks. Initially we considered placing this species to the genus Virpazaria due to the thickened parietal callus, which was mentioned in the original description of the genus Virpazaria. However, the subcircular/triangular aperture indicates that it is better to be placed in Spelaeodiscus.
Formerly, this population was incorrectly referred to as S. albanicus and was taken into consideration in that species' Red List assessment (Reischütz and Fehér 2017) Conservation status. To our present knowledge this species is very rare (currently known from a single location) and thus AOO is smaller than 20 km 2 . However, there is no reason to suppose that AOO, EOO, number of locations, number of subpopulations or the number of mature individuals are declining or extremely fluctuating. Therefore, it might be assessed as Near Threatened (NT).

Species recognition and biogeography
We examined all available Spelaeodiscus samples from the Western Balkan area (Slovenia, Montenegro, Albania). Our main aim was to delimit (sub)species based on conchological characters. We found that shell size, spire height and rib density is particularly variable within and between populations, and can be used only with caution for species recognition. Morphology of ribs, however (elevated or low, thin, lamella-like or strong, calcareous), the fine sculpture of the protoconch (glossy or granulate), and the obliqueness of the aperture to the shell axis are useful character in several cases. The two subspecies described here (S. albanicus edentatus ssp. n. and S. unidentatus acutus ssp. n.) are primarily recognized based on differences of the apertural teeth. The most important traits distinguishing the species delimited here are hardly or not quantifiable. Thus, no statistical tests are applied to verify our taxonomic decisions. We are aware of the limitations of the exclusively conchological approach, especially in case of species known from single shells or single populations. However, given the commonness of rarity, omitting the description of singletons would prevent the description of a very significant proportion of the species-level diversity (Lim et al. 2012).
Spelaeodiscus dejongi has the largest known area and is known from most numerous populations. In face of the large variability between populations we found no qualitative traits that would distinguish populations on species or subspecies level, therefore we treat it as a single, variable species. However, future studies should focus on the degree of differences on molecular level.
Although the majority of species is known from multiple populations of relatively large areas, three single-site endemic species (S. densecostatus sp. n., S. hunyadii sp. n., S. latecostatus sp. n.) are also described. The latter two new species were found in sympatry with the widely distributed S. dejongi, which is an evidence that none of them are conspecific with S. dejongi (see Table 2). More precise field collections should focus on the area they inhabit in order to examine the true extent of their range.

Habitat
Spelaeodiscus (in contrast to Aspasita) is obviously a subterranean genus. Up to the recent past, only a few populations were known and it was believed to be troglobiont, because -if not in fluvial flotsam -all findings were from or near caves. In the past decade, some other gastropod taxa, previously believed to be troglobiont, turned up in non-carbonate areas, or in limestone but assuredly outside of caves (Deli and Subai 2011, Subai 2011, Dedov 2015Reischütz et al. 2016). These findings already demonstrated that Agardhiella Hesse, 1923, Gyralina Andreae, 1902, Sciocochlea C.R. Boettger, 1935and Tsoukatosia Gittenberger, 2000 have affinity to the superficial underground compartments (also known as "Mesovoid Shallow Substratum" or "Milieu Souterrain Superficiel", widely abbreviated as MSS, see e.g. Juberthie et al. 1980Juberthie et al. , 1981Camacho 1992;Culver andPipan 2009, Mammola et al. 2016).
We have collected all Spelaeodiscus samples in fissures or small cavities of bare limestone cliffs, from which fine granulated material could be yielded. Although we have found only empty shells, and therefore it is still not completely clear where they actually live, the abundance of Spelaeodiscus in these superficial fissures seems to be larger than in cave deposits. This prompted us to question whether Spelaeodiscus is truly troglobiont.
Literature data are very scarce about MSS dwelling gastropods, and still, that little is dealing mostly with scree slopes, habitats where fragments of rocks are accumulating at the bottom of rocky walls, and are covered over time by an evolving soil (Arndt  and Subai 2013, Rendoš et al. 2014. Scree slopes were reported to harbour exclusively edaphic species, but Arndt and Subai (2013) presume that this was due to the applied passive sampling method (buried pitfall traps), which is ineffective for catching small sized and immobile snails. Our sites represent a different sort of habitat type, similar to "bedrock MSS" according to the subdivision of Mammola et al. (2016), except that the rock surfaces of these sites are not covered by an evolving soil. Due to the nature of this habitat type, the use of pitfall traps or other sort of passive sampling devices was out of question. Therefore, we stayed with the "scratch and sieve" or "scratch and flotate" approach, i.e. we scratched out fine granulate material from the superficial fissures of rocks applying long and narrow hand rakes (Fig. 15A-B) and separated the shells by sieving or by flotation (Fig. 15C-E).
It is still disputed whether such a bedrock MSS habitat is characteristically different from caves or it can be considered just as the extension of the cave system, and therefore, its fauna is composed of troglobionts of wider ecological tolerance or there are certain specialized elements exclusive of MSS (see Mammola et al. 2016 for review). The role of Spelaeodiscus remains unclear in this respect. However, our study indicates that the bedrock MSS habitats in the Balkans harbour a large and still largely undiscovered gastropod diversity.