In the present study a comprehensive investigation of the genus Siciliaria Vest, 1867 (type species: Clausilia grohamnniana Rossmässler, 1836) was performed, including morphology of the genital organs and DNA sequence analyses, which were interpreted in the light of the current taxonomic system (Nordsieck 2007, 2013a; MolluscaBase 2021). In addition to Siciliaria (sensu MolluscaBase 2021), 14 taxa belonging to genera related to Siciliaria (namely Charpentieria, Stigmatica, Gibbularia, Papillifera and Mauritanica) were included in the molecular genetic study as a first attempt to elucidate their relationships using Papillifera as outgroup. Yet, we were well aware that the low number of samples would provide only a preliminary insight. We systematically introduced new genital anatomical characters for the above listed genera. This study follows the strategy and methods of the recently published integrative approach to the taxonomy and systematics within Montenegrina Boettger, 1877 (De Mattia et al. 2020; Mason et al. 2020a), where DNA-based phylogenetic trees together with morphological characters (both shell and morphology of genital organs) were the basis for a taxonomic revision.

A atrium;

ALPP anterior lower palatal plica;

AUPP anterior upper palatal plica;

BC actual bursa copulatrix;

CP clausiliar plate;

CS clausiliar stalk;

CSP cross section of the penial pseudopapilla;

CSE cross section of the epiphallus;

D diverticulum of the bursa copulatrix;

E epiphallus;

EF epiphallar funnel;

ELP epiphallar longitudinal pleats;

ER epiphallar ring;

ETLP epiphallar transitional longitudinal pleats;

EO epiphallar outlet of the hemipapilla;

ET epiphallar thickening;

FDBC first duct of the bursa copulatrix;

FELP free epiphallar longitudinal plate;

FO free oviduct;

H _a aperture height;

H _s shell height;

HG hermaphroditic gland;

H _s shell height;

IOP internal sculpturing of penis;

IL columellaris or inferior lamella;

L lunella;

OELP occupied epiphallar longitudinal plate;

OS ovispermiduct (second hermaphroditic duct);

P penis;

PC penial complex (P+E);

PCL penial complex length;

PG prostatic gland;

PLL parallelis;

PP penial pseudopapilla;

PPP parapseudopapilla;

PR penial retractor muscle;

PRI principalis;

PUPP posterior upper palatal plica;

SCL subclaustralis;

SCOL subcolumellatis;

SDBC second duct of the bursa copulatrix;

SG sperm groove;

SPL spiralis;

spm specimen(s);

SUL sulcalis or parietalis;

SUT suturalis;

TP transition passage;

V vagina;

VD vas deferens;

VR vaginal retractor;

W _a aperture width;

W _s shell last whorl width (body whorl).

CWDM malacological collection of Willy De Mattia;

NHMW Natural History Museum Vienna (Naturhistorisches Museum Wien);

SMF Senkenberg Museum Frankfurt.

In the first part of the Results we describe the molecular genetic data. For clarity, and in view of the various taxonomic changes in the past, a comprehensive table is presented at the end of the taxonomic part including the new full checklist of the taxa so far considered as Siciliaria (Table 12). In the following, we refer to these taxa as belonging to “Siciliaria/Sicania“. We decided to apply the new taxonomic system already in the phylogenetic trees and their discussion, as well as in the morphological descriptions of the taxonomic part. In the general discussion we interpret the molecular and anatomical results and give an overview on the, so far, unidentified or enigmatic taxa mentioned in the literature.

The taxonomic part of the results comprises the descriptions of the taxa with a detailed list of examined specimens and the principal systematic and/or faunistic publications. For the specimens investigated genetically, the identifier is listed together with the GenBank accession numbers (in square brackets) for sequences of the mt cytochrome c oxidase subunit 1 gene (COI) and where available for the internal transcribed spacer 2 (ITS2). The descriptions of the shells and the clausiliar apparatus of those taxa that are currently valid (MolluscaBase 2021) were already provided and discussed by Nordsieck (2013b). We report here only the descriptions provided by Nordsieck (2013b). For the newly described taxa, the shell and clausiliar apparatus are described with full details.

The collection numbers, voucher numbers, GenBank accession numbers and geographical coordinates for the specimens used in the molecular genetic analyses are listed in Table 1. Papillifera was used as outgroup for the phylogenetic trees calculated from the three data sets (COI, ITS2, combined). BI and NJ analyses yielded the same overall topologies (not shown). The BI tree based on COI sequences comprising 92 individuals is shown in Figure 4. In this tree, the species from northwestern Sicily so far comprising the genus Siciliaria were found within two separate highly supported main clades. Albeit the two clades (I and II) emerge as sister groups in the combined tree, this grouping is not well supported, and it remains unclear whether Siciliaria and Sicania together form a monophylum. There is only one exception, Siciliaria scarificata (in the tree designated as Mauritanica scarificata comb. nov.), which forms the sister group of Mauritanica perinni polygyra. This branch is the sister clade of clade II, although this relationship is very weakly supported. The mean p distance between clades I and II was 19.6% (range 18.9–21.6%). The two clades correspond to the division into the two genera Siciliaria and Sicania as proposed by Boettger (1877).

The taxa comprising the two main clades I and II cluster in a geographic pattern (maps in Fig. 1E, F). Clade I includes species that are found in limited areas in the eastern part of the distribution area, plus the widely distributed Siciliaria calcarae. The latter is found in several occurrences in the southern parts of the distribution range from west to east. Along the eastern part of its distribution area, the nominate subspecies of S. calcarae is sometimes replaced by local costate forms. Clade II comprises the western species distributed in a comparatively small area from San Vito Lo Capo Peninsula, Monte Cofano to Cornino-Custonaci area. Within the main clades, the various (generally highly supported) subclades are mostly consistent with taxa and reflect their distribution. Specimens from the same locality delivered very similar or identical sequences. Intraspecific distances (summarised in Table 3) within both Siciliaria and Sicania were moderately low mean distances up to 7.0% with the highest values found in S. calcarae (7.0%) and S. grohmanniana (5.1%). Besides the main clades I and II, the tree contains several quite distinct lineages representing other taxa [belonging to Stigmatica, Charpentieria, as well as Gibbularia, which are separated by high p distances from each other (mean distances ranging from 18.6–23.8%), as well as from clades I and II (18.3–23.1%). In this tree, the genera Stigmatica and Gibbularia are not monophyletic. Charpentieria forms one clade but the support values are very low. The relationships between the two main clades and the other genera remain unresolved and appear as a polytomy in the tree. The low resolution in the deeper nodes is not surprising given the high distances, as substitutional saturation might blur the relationships among lineages. The average p distance between the outgroup Papillifera and the ingroup sequences was 24.6% (range of means between groups 23.8–25.6%). Even within some genera remarkably high distances were found (up to 25.8% Papillifera, 22.6% Charpentieria itala, 18% Charpentieria stenzii), while distances within Siciliaria and Sicania were lower (mean p distance 13.4 and 11.4%, respectively) (see Table 2).

The ITS2 sequences were obtained from 42 individuals (Table 1) and comprised altogether 106 sequences (due to up to five cloned sequences per individual; see Materials and methods). The BI tree (Fig. 5) shows all sequence variants isolated from those individuals. The variation among ITS2 copies is due to the fact that for some individuals, more than one clone was sequenced (due to the genomic arrangement of the rRNA genes in repeats of clustered units, more than two alleles can be expected). Generally, small distances were found among ITS2 sequences, resulting in a low resolution in the ITS2 tree. Most branches did not obtain sufficient support, but the tree reflects to some extent the COI tree. The western taxa (corresponding to main clade II, Sicania) appear as separated group including no representatives of main clade I (Siciliaria). One subgroup contains only S. nobilis and the other subgroup contains S. crassicostata, S. eminens, and a few sequences of S. nobilis (from San Vito). Various clones of S. crassicostata differed slightly and for the specimen 33, clones 2 and 3 appeared in a subclade separate from the remaining sequences of S. crassicostata (including those from the same individual). The taxa corresponding to main clade I are found within several mixed clades/haplogroups with no apparent taxonomic or geographic pattern. Sequences from specimens of the same population cluster together with low distances. Sequences of the other genera appear as various separate branches. Stigmatica and Gibbularia are not monophyletic.

The tree based on the combined data set (COI plus ITS2; 45 individuals) is shown in Fig. 6. It has the same overall topology as the COI tree, but with high support of several nodes, but fewer individuals represented. The apparent sister group relationship between clades I and II received no considerable support and thus, the relationship between the two clades remains open. The species are monophyletic and most of them well supported. Concerning the other genera, it should be mentioned that this tree provides less information as the number of individuals is lower than in the COI tree. As in the COI tree, C. stenzii and C. itala/dyodon cluster, highly supported, but in the combined tree of this clade only C. stenzi and C. dyodon were included. Mauritanica (including the former S. scarificata) is highly supported as well.

Specimens from the same locality delivered very similar or identical sequences. Intraspecific distances (summarised in Table 3) within both clades I and II (i.e., Siciliaria and Sicania) show moderately low mean distances, up to 7.0% with the highest values found in S. calcarae (7.0%) and S. grohmanniana (5.1%). With one exception, all species were highly supported in the COI tree and in the combined tree. Within Siciliaria/Sicania only S. calcarae was found in two subclades, which formed together with Siciliaria leucophryna an unresolved trichotomy within one clade. In some cases, subspecies formed slightly separated lineages (e.g., Siciliaria tiberii tiberii), while generally this was not the case.

The taxa comprising the two main clades I (Siciliaria) and II (Sicania) cluster in a geographic pattern (maps in Fig. 1E, F). Most taxa show well defined and delimited distributions, with some exceptions (of both Siciliaria and Sicania). The widely distributed Siciliaria calcarae has a partially overlapping distribution with either Sicania n. nobilis or Sicania eminens. Moreover, along the eastern part of the distribution area, the nominate subspecies of Siciliaria calcarae is locally replaced by other subspecies that differ by virtue of the costate shells or details of the clausiliar apparatus. The distribution records of Sicania crassicostata and Sicania eminens overlap in a small area near Contrada Scurati/Grotta Mangiapane, where the two species are, hardly distinguishable by their shell but show differences in the morphology of the genital organs and the genetic results (see Sicania eminens comb. nov.).

Siciliaria leucophryna shows a narrow distribution, limited to Isola delle Femmine, Pizzo Mollica, and Pizzo Manolfo. Siciliaria tiberii is restricted to the calcareous massif of Monte Palmeto, Pizzo di Mezzo, Monte Pecoraro and Montagna Longa and its northwestern coastline. Siciliaria ferrox occurs in the Trabia-S. Onofrio area. The closely related Siciliaria grohmanniana and Siciliaria septemplicata are indeed geographically close, the former occurring exclusively along the southern slopes of Monte Gallo and on Monte Pellegrino and the latter found along the northern slopes of Monte Gallo and scattered localities south of Palermo (Nordsieck 2013b). Syntopy seems to be very rare among Siciliaria/Sicania taxa. To our current knowledge, Siciliaria calcarae is sympatric with Siciliaria septemplicata (south and west of Palermo area), with Siciliaria grohmanniana (Monte Pellegrino), with Sicania eminens (Custonaci and Castellammare del Golfo Area) and with Sicania nobilis (San Vito lo Capo area). The sympatry of Siciliaria calcarae and Sicania crassicostata from Favignana Island seems to be due to antropochorous dispersal of the latter taxon. The southern part of the Siciliaria/Sicania distribution area so far seems to be occupied only by Siciliaria calcarae as also supported by the molecular genetic results. In one locality only (Castelluzzo) Siciliaria calcarae and Sicania nobilis were found together at the same spot: shady limestone walls in a Quercus ilex shrub. Nonetheless, a clear ecological niche separation of these two taxa syntopic at this locality was detected. The actual and detailed distribution ranges of the Siciliaria taxa still have to be clarified. Moreover, further field research must still verify undetermined or uncertain old literature citations, and thoroughly investigate a diverse and heterogenous territory with an amazing endemism rate.

Siciliaria/Sicania taxa show a remarkable adaptation and capability to colonise not only dry, open and exposed limestone walls and cliffs but also a huge variety of habitats and ecological niches. The most stenoecious species are, in order, Sicania nobilis, Siciliaria ferrox, and Siciliaria septemplicata, which are found exclusively on limestone walls or limestone boulders. Sicania crassicostata is found on limestone walls or under rocks. More euryoecious habits were recorded for Siciliaria grohmanniana grohmanniana, which is found on exposed limestone walls hiding in cracks and under crags. It is also found in Pinus sp. forest on decaying woods and tree trunks, including shady and humid spots on mosses and ferns. Interestingly, its subspecies Siciliaria grohmanniana addaurae ssp. nov. is found exclusively on limestone walls. Siciliaria leucophryna and Sicania eminens colonise limestone cliffs hiding in cracks or under stones. They are very common on isolated boulders and tree trunks and barks in the xerophilic scrub. The most euryoecious species is Siciliaria calcarae, which colonises all the habitats until now described but also is commonly found in anthropogenic environments as stone walls, road walls, ruins and disturbed habitats.

The high number of Siciliaria/Sicania specimens dissected during this study (n = 120) provided an accurate overall description of the genital organs of these genera.

No seasonal variations were detected concerning shape or internal sculpturing of genital organs. The only clear distinction was between adult specimens with full-developed genital organs and immature, subadult specimens with extremely reduced, vestigial genital organs.

The general external morphology of the genital organs is the same in all taxa of Siciliaria/Sicania. The relative dimensions (ratio between the shell height and the length of the penial complex H_s/PCL×100) do not substantially differ among taxa, ranging from 25% to 35%, revealing a great dimension stability of genital organs in relationship to the shell dimensions. The genus Montenegrina (De Mattia et al. 2020) showed a higher variability, ranging from 13.9% to 87.6%. The overall appearance of the genital organs of Siciliaria/Sicania is always balanced [“mesomorphic” as defined in De Mattia et al. (2020)], without showing the extreme variability found in Montenegrina where extremely elongated and thin or short and bulky genital organs were found.

The hermaphroditic gland (HG) has many consolidated acini and it is found along the two apical whorls of the animal’s body. The first hermaphroditic duct (FHD) is very thin along its proximal portion but abruptly turns into a highly coiled, skin-like structure. The diameter of the FHD is much larger along the coiled part, and the number of whorls ranges from six to eleven. The distal uncoiled part of the FHD is very thin, straight and ends directly in the fertilisation chamber-spermatheca complex. The albumen gland (AG) is slender. The general scheme of the FHD is stable among all the Siciliaria taxa. The AG is very variable in size compared to the ovispermiduct (OS). In full-grown adult specimens, it can be larger or as long as the OS or barely reaching ¹/₄ of its length. The OS consists of a female and a male part including the seminal groove, which is not visible from outside. Externally, it is irregularly spaced by smooth constrictions and it is whitish to cream in colour. The male, prostatic part consists of the visible prostatic gland (PG) and the sperm groove (SG), light to dark grey in colour and clearly distinguishable from the lighter female part. The overall size of the OS is very stable among the Siciliaria/Sicania taxa. The free oviduct (FO) is usually thin and long and its length is stable in relation to the length of the vagina (V), and its average ratio (FO/V) is ~ 1. The V is simple, usually cylindrical, without any appendix or caecum. The vaginal retractor (VR) is strong; it is always present and attached to the second duct of the bursa copulatrix (SDBC). It was not depicted in the anatomical drawing due to its low taxonomic value. The V is stable in length in relation both to shell height and penis length. The ratio between the length of the penial complex (PC) and the length of the V (PC/V) is also stable, ranging from two to three. The BC+SDBC complex (CBC) consists of the FDBC, a second duct (SDBC), a well-developed D (diverticulum) and the actual BC+SDBC. The D is always longer than the SDBC+BC. The transitional section between the BC and the SDBC can range from clearly visible to completely missing (with all degrees of transitional states). The PC comprises the penis (P) and the epiphallus (E). The transition between P and E does not always show the epiphallar thickening (ET), as stated in Nordsieck (2013b). More than 50% of the dissected specimens did not present the ET. The presence of the ET is not species-specific as it is randomly present or missing also in specimens of the same population of one given taxon. The flagellum is absent. The retractor muscle (RM) is single and undivided and usually strong. The P is usually uniformly cylindrical or slightly swollen proximally, without caecum or penial appendix. The E is usually as long as the P. It can be cylindrical to thin and spindly. The transitional area between the E and the distal portion of the vas deferens (VD) is usually smooth or barely visible. The atrium (A) is usually large and short.

In contrast to the external morphology of the genital organs, the internal sculpturing differs between the various taxa of Siciliaria and Sicania, but is stable within the taxa, with only minor population/individual variability. The penis shows the highest variability, which involves the combination (or the absence) of pleats arranged in a longitudinal, transversal, or oblique direction or creating irregular patterns. The epiphallus shows different types of sculpturing, with longitudinal pleats or without any structure. The internal transition between the epiphallus and the vas deferens is very clear due to the clear change of the sculpturing. The structure and the variability of the penial pseudopapilla and the morphology of the internal transition between penis and epiphallus will be discussed in detail in the following. The atrium can exhibit different configurations, from completely smooth to variable pleats. In contrast to what was found in Montenegrina (De Mattia et al. 2020), a large atrial fold has never been detected. The internal V shows few different configurations. Similar to the penis, its variability lies in the combination (or absence) of pleats arranged either in a longitudinal, transversal or oblique direction.

Two specimens were found with the spermatophore intact and embedded into the diverticulum of the bursa copulatrix complex or in the vagina and partially inside the first duct of the complex of the bursa copulatrix. The spermatophore of Siciliaria calcarae calcarae (Philippi, 1844) and Mauritanica perinni polygyra (O. Boettger, 1879) are described for the first time. The spermatophores are slender and slightly longer than the diverticulum. The overall shape is slightly to markedly bent. These preliminary observations revealed a difference between Siciliaria with both upper and lower keel and Mauritanica with only the upper keel.

All the genera Siciliaria, Sicania, Mauritanica, Stigmatica, Gibbularia, and Papillifera exhibit a pseudopapilla. The pseudopapilla (PP) is a “false” penial papilla, found at the transition between the penis and the epiphallus, slightly distally to the insertion of the retractor muscle. The pseudopapilla, conversely to the actual penial papilla [as in the genus Montenegrina, depicted in De Mattia et al. (2020)], originates from one side of the penial wall and totally lacks a penial channel. Its lumen is filled with loose spongy tissue (Fig. 3.6). The shape and dimensions of the pseudopapilla are extremely variable, from conical and blunt to elongated and cylindrical. Sometimes it is extremely reduced or totally missing. Presumably the absence of the pseudopapilla represents the apomorphic state. The base of the pseudopapilla can be simple, thus it directly originates from the penial wall. Otherwise, the pseudopapilla can originate from a fleshy structure emerging from the penial wall. This structure is circular, fleshy, ring-like, usually smooth and more or less robust. We name this genital structure “epiphallar ring” (ER). The ER can be missing or up to three. When detectable from outside, the transition between penis and epiphallus presents a more or less sudden narrowing of the proximal penis, distally to the base of the retractor muscle and corresponding to the area where the pseudopapilla originates. The genital portion immediately distal to the narrowing could be seen as a thickening and could represent what Nordsieck (2013a) introduced as the ”epiphallar thickening“ (ET).

In Siciliaria/Sicania one to three strong epiphallar rings are always present (only one being the origin of the pseudopapilla). Charpentieria and Stigmatica present only one epiphallar ring which is the origin of the pseudopapilla. In Gibbularia the epiphallar ring was found only in Gibbularia gibbula cf. sanctangeli (Fig. 56.6). Papillifera never shows an epiphallar ring and the pseudopapilla is either isolated (thus directly originating from the wall) or directly originating from the distal end of one epiphallar longitudinal pleat.

In the Southern Alpine Charpentieria the genital investigations revealed two undescribed structures of the transition between P and E: in C. dyodon s. l. it is named “parapseudopapilla” (PPP) and in C. stenzii s. l. it is named “hemipapilla” (HP) and are described in the following sections. In order to describe and classify the huge variety of PP-ER-ELP combinations found in all the taxa, we created a pseudopapillar formula. This formula will be provided for each taxon and population dissected, in order to highlight the extreme variable situation of this part of the genital organs. In this formula the parentheses () mean direct connection (continuity/contiguity of anatomical traits), whereas the plus + means interruption of the anatomical continuity. For example, the formula 1ER(PP)+2ER(ELP) means that PP originates from the distal (first) ER and the proximal ER (second ER) is directly connected with the ELP.

Shell. Shell elongated, fusiform, sinistral, can be either decollate or non-decollate, with or without well-developed white surface layer. Apex subacute when present, whitish to dark brick red in colour. Protoconch smooth. Spire slowly and regularly growing with 9.5–11.5 whorls. Umbilicus closed, sutures shallow. Aperture subovoid to subquadrangular. Peristome continues to be interrupted. Average shell height 19.9 ± 2.1 mm (n = 630, decollate and not decollate shells), average last whorl width 4.5 ± 0.4 mm (n = 630), average aperture height 4.6 ± 0.5 mm (n = 630), average aperture width 2.9 ± 0.4 mm (n = 630). Whorls weakly rib-striated, rib-striated, ribbed to percostate without or with evident to barely recognisable sutural papillae. Dorsal keel missing, mostly indistinct to prominent. Lunella always present, dorsal to dorso-lateral, more or less developed. Inferior lamella low, moderately high, high to very high. Missing, one or two anterior upper palatal plica; when two are present: upper one mostly separated from upper palatal plica; when one is present: separated from or connected with upper posterior palatal plica. Rarely, lower anterior upper palatal plica is present, separated from or connected with upper palatal plica. ALPP tending to be shortened to almost missing. Spiralis overlapping or not overlapping parietalis. Posterior lower palatal plica missing more or less reduced. Palatal edge of clausilium plate distally receding, slightly or not receding. Clausilium palatal edge against distal end not bent upwards, or bent upwards to strongly bent upwards.

External distal part of the genital organs. Free oviduct slightly shorter to remarkably longer than the vagina. Vas deferens thin. First duct of the bursa copulatrix slightly shorter to much longer than second duct of bursa copulatrix + the actual bursa. Distinction between the actual bursa and second duct of bursa copulatrix clear to missing. Diverticulum of the bursa copulatrix longer to much longer than the vagina and second duct of bursa copulatrix + the actual bursa. The vagina is long or short and the atrium usually large. Penial complex always longer to much longer than the vagina. Retractor muscle short to long, usually robust. Epiphallar thickening present or missing. Epiphallus slightly shorter to much longer than the penis. Transition between epiphallus and vas deferens clearly visible to totally indistinguishable.

Internal distal part of the genital organs. Vagina and penis with internal sculpturing comprising a combination (or also absence) of pleats of different size and texture, arranged in a longitudinal, transversal or oblique direction or creating particular net-like pattern. Atrium simple or pleated. Pseudopapilla originating from epiphallar wall or epiphallar ring, elongated to roundish, with smooth or coarse surface. Epiphallar rings up to three to completely missing. Proximal epiphallar ring connected or not with the epiphallar pleats. Epiphallus with or without longitudinal pleats, both smooth or fringed. Epiphallar walls almost smooth, finely granulated of with small transverse papillae.

The principal rationale of our integrative strategy was whether phylogenetic relationships confirm morphogroups found in a specific area and whether or not they correspond with current taxonomy. We deliberately refrained from applying automated species delimitation methods, for which larger sample sizes would have been necessary. Furthermore, in various land snail species as it was shown such methods may deliver discordant results (e.g., Prevot et al. 2013; Modica et al. 2016; Batomalaque et al. 2019; Mason et al. 2020a), there may be a lot of factors hampering straightforward delimitation solely based on genetic clades and the concept of the DNA barcoding gap (Meier et. al. 2008). First, intra specific distances were found to vary considerably among various land snail species and are sometimes higher than commonly reported interspecific distances (Davison et al. 2009). Further examples for high intraspecific distances are the clausiliid genera Montenegrina (Mason et al. 2020a) and Clausilia (Mason et al. 2020b), the genus Schileykula (Harl et al. 2019) and the genetically highly diverse hairy snail Trochulus hispidus where even budding speciation was observed (Kruckenhauser et al. 2011).

So far, mostly mitochondrial marker sequences were used successfully in phylogenetic studies of land snails. The quite frequently used nuclear encoded histone genes H3 and H4 (including the spacer region in-between) often did not add much information or even resulted in confusing trees, probably due to multiple paralogous copies of these genes that escaped homogenisation and/or recombination events after hybridisation (e.g., Harl et al. 2019; Mason et al. 2020a). Indication for interspecific hybridisation, even (at least sporadically) over wide phylogenetic distances were reported for several species, e.g., in the clausiliid genus Montenegrina (Mason et al. 2020a). Further examples were found e.g., in the bradybaenid land snail genera Ainohelix and Ezohelix (Morii et al. 2015) or the orculid genus Schileykula (Harl et al. 2019). Likewise, the internal transcribed spacer ITS2 used in the present study did not yield a well resolved tree and showed too low variation to unambiguously elucidate the phylogenetic relationships within Siciliaria and Sicania. Anyhow, several mt lineages were confirmed in the ITS2 tree. The ITS2 marker sequence showed some problems caused by paralogous copies as indicated by the various positions the sequences from single individuals took in the tree. Based on the presently available data it cannot be decided whether this is solely due to incomplete lineage sorting. Intraspecific hybridisation would result in similar patterns and there are some cases where this explanation appears likely (e.g., alcamoensis; see Taxonomic part).

In summary, in the COI tree the species were monophyletic except the widely distributed S. calcarae. Clustering of subspecies is mentioned in the taxonomic part, albeit this aspect is of minor relevance, (1) because subspecies would not necessarily be expected to be monophyletic and (2) because they were represented by too small samples.

Potiez and Michaud (1838: 181–182) introduced Clausilia decollata and Clausilia deshayesii with a broad distribution indication: ”Hab. La Sicilie“. These names probably belong to Siciliaria/Sicania, but their specific status was not yet clarified. Benoit (1876: 151; 1881: 106) mentioned Clausilia deshayesii, providing a precise distribution (“vive nelle campagne di Palermo; l’abbiamo pure ricevuta dai dintorni di Prizzi”). As synonyms, Benoit (1876) listed Clausilia calcarae, Clausilia assimilis (= ?) and Clausilia castanea (= ?) and Benoit (1881) listed Clausilia calcarae, Clausilia septemplicata and Clausilia castanea (= ?) thus, as already suggested by Nordsieck (2020: 6) this name could be regarded as a junior synonym of Siciliaria calcarae or Siciliaria septemplicata. As a matter of fact, both taxa are known to occur in the surroundings of Palermo. On the other hand, Prizzi is currently considered remarkably outside of the known distribution of Siciliaria/Sicania, and further research in this area is needed in order to clearly assess the identity of this name. Its synonymy with Clausilia calcarae and Clausilia septemplicata can only be speculated until additional data are available. Benoit (1876, 1881) introduced three taxa that currently are unidentified. The first is Clausilia trinacrina (Benoit 1876: 151) or also cited as Clausilia trinaclina (Benoit 1881: 105), erroneously cited by Nordsieck (2013b: 4) as C. trinacliana that he arbitrarily considered as a misprint of trinacriana. The distribution of this taxon (Benoit 1881: 106) is the area surrounding Palermo and Calatafimi. De Stefani (1895: 186) cited the species with its proper name, which is Clausilia trinacrina, as he received the correct name spelling directly from Benoit: “nel detto catalogo (Benoit 1881) Benoit la chiama trinaclina, ciò per errore di stampa come risulta dalla correzione a penna fatta da lui stessa nella copia donatami”. Moreover, De Stefani (1895: 187) provided a precise locality for the species: Monte Cuccio near Palermo. The differential diagnosis provided by Benoit and Boettger’s opinion (Boettger 1881: 106) makes the synonymy with Siciliaria calcare very plausible. Benoit (1876: 151) cited Clausilia panormitana from Monte Cuccio, east of Palermo as a synonym of Siciliaria grohmanniana. Our field research confirmed that Siciliaria grohmanniana is not present on Monte Cuccio and its surrounding peaks. For Clausilia trinacrina, the synonymy with Siciliaria calcare is very plausible.

Finally, Benoit (1876: 152) cited Clausilia laudabilis from San Fratello. This locality is probably and old toponym from the surroundings of Bagheria (Palermo) as San Fratello near Messina is totally out of the distribution range of Siciliaria/Sicania. Clausilia laudabilis is considered by Nordsieck (2013b: 7) as a synonym of Siciliaria leucophryna despite the locality provided by Benoit doesn’t match with the current known distribution of this species. Thus, both the exact position of the locality and the identity of Clausilia laudabilis remain to be assessed.

Benoit (1881: 117) introduced also Clausilia rubra from San Fratello, and San Fratello near Messina cannot be excluded in this case. Clausilia rubra Benoit, 1881 could be referred to Stigmatica incerta (Küster, 1861), which is known to occur from the area (WDM personal data). Despite Boettger’s opinion that considered Clausilia rubra as a form of Siciliaria septemplicata, Benoit (1881: 117) disagreed with his opinion, by virtue of a differential diagnosis that highlights important differences. The given locality is found remarkably outside of the currently known distribution of both, Siciliaria and Sicania (Nordsieck 2013b: 2). More field and taxonomical research are needed in order to properly assess the status of this species and, at the moment, no synonymy is conceivable.

Clausilia subdiaphana was introduced by Benoit (1881: 118), who stated that this taxon is conchologically similar to Siciliaria grohmanniana but differs by a different arrangement of the lamelle and plicae and by a very fragile, not decollate shell. The collecting locality is ”montagna Buon Riposo presso Palermo”. This old toponym is currently almost forgotten, but Scinà (1818: 51, 57) identified this hill at the western foot of Monte Cuccio, east of Palermo. Yet, the lithological substratum of that hill and its surroundings is composed by quartzite, gres, and sandstones, thus an unusual habitat for Siciliaria/Sicania. The fragile shell could represent an adaptation to a soil extremely poor in limestone contents. Monterosato (1894: 170) assumed the snails from Monte Pellegrino to be ”Var. ex forma: subdiaphana, Ben.”, a variety of Siciliaria grohmanniana. Monterosato neither justified the synonymy, nor stated that he actually found Benoit’s taxon at Monte Pellegrino. At the moment, no synonymy is conceivable.

The status of Siciliaria riberothi, introduced by Brandt (1961: 8 as Siciliaria leucophryna riberothi) was thoroughly discussed by Nordsieck (2013b: 14). The taxon is based on a specimen provided by Monterosato labelled as Clausilia riberothi, collected from a valley north of Ribera (Agrigento) (currently outside of the known distribution of Siciliaria and Sicania), housed at the Senckenberg Natural History Museum (SMF 163947). This specimen was depicted by Brandt (1961: 20–21). Brandt (1961: 8), as additional material, listed a ”Paratypoide“ from his own collection (Cl. 2518/5) but the origin of this sample(s) is not specified. Probably, the collecting data provided by Monterosato on the original label was wrong as was also stated by Beckmann (2004: 188) after a field survey.

Nordsieck (2013b: 5) depicted another specimen from Monterosato’s collection, labelled as Clausilia remota (SMF 232084) collected by Monterosato from an unidentified locality, namely Monte della “Terrazza” or “Torrazza”. As stated by Beckmann (2004: 188), it is unlikely that this locality is Torrazza, east of San Vito lo Capo as from this locality only Siciliaria calcarae and Siciliaria nobilis were found. Considering the overall shell shape, the prominent dorsal keel and the arrangement of the plicae and lamellae (AUPP and ALPP developed and visible from the frontal view of the mouth), both Siciliaria riberothi and Monterosato’s samples from Monte della “Terrazza” or “Torrazza” could be provisionally referred to Siciliaria tiberii ssp.

The concept of interspecies hybridisation (or geographic forms) introduced by Nordsieck (Nordsieck 2007: 99–101; 2013b: 10) refers to populations that share certain shell characters and have to some extent overlapping distribution [such as calcarae-septemplicata (e.g., Parco, south of Palermo; Sagana near Borghetto), septemplicata-grohmanniana (Punta Priola), tiberii-calcarae (Monte della Fiera), leucophryna-calcarae (Sferracavallo), crassicostata-eminens (Monte Cofano) etc]. When available, such populations were analysed anatomically and genetically in the present study. Hybridisation and gene flow proved to provide no suitable explanation for sharing common shell characters. The results did not support close relationships or hybridisation between these taxon pairs. The “hybridisation” cases will be discussed taxon by taxon in the taxonomic part.

Infraordo Clausilioidei Gray, 1855

Superfamilia Clausilioidea Gray, 1855

Familia Clausiliidae Gray, 1855

Subfamilia Alopiinae A.J. Wagner, 1913