Papillifera bidens (Linné 1758) (Clausiliidae, Alopiinae), a common, but little known species

Hartmut Nordsieck (VI.2011)

I. Introduction

The genus Papillifera Hartmann 1842, which belongs to the subfamily Alopiinae and the tribe Delimini (Nordsieck 2002, 2007), includes two species, P. bidens (Linné 1758) and P. solida (Draparnaud 1805). Both originate from Italy; while P. bidens is widely distributed in the Mediterranean, P. solida has been found beyond Italy only in southern France (Provence). Both species differ mainly by the dark subsutural band of the shell, which is characteristic for P. bidens and absent in P. solida.
Though P. bidens is known as a species since a long time, the knowledge of its various forms and subspecies is poor. The wide distribution untypical for a clausiliid with its striking restriction to human settlements has not been explained so far. While 19th century malacology had achieved at least a basic knowledge of the forms of this species (chapter II), modern malacology, except for an unnecessary dispute on the species' correct name (chapter IV), supplied almost no further information on its intraspecific diversity and no explanation of its extraordinary distribution (chapter III).
The results of the author’s own research of P. bidens in Italy and other Mediterranean countries are summarized in the chapters V and VI.

II. History

P. bidens has been diagnosed and figured by Rossmässler (1836: 12, pl. 12, figs. 169-170) under the name Clausilia papillaris (Müller). Additionally to the type form he described a variety C. p. var. virgata "Jan" from "Oberitalien" (: 12, fig. 170) with the following diagnosis: "testa costulato-striata, peristomate continuo; palato calloso; cervice basi in cristam compressa". This diagnosis, with the exception of "palato calloso", corresponds with the definition of P. b. affinis = virgata, which resulted from my own research (chapter V).
Philippi (1836: 139, pl. 23, fig. 30) separated Clausilia affinis from C. papillaris with the diagnosis "sutura concolore et striis elevatis sublamellaribus". Later on, the same author (1844: 116) united C. affinis and C. p. var. virgata to his C. papillaris var. β, for which he repeated Rossmässler's diagnosis of C. p. var. virgata.
L. Pfeiffer (1848: 453-454) listed the species as C. bidens (Linné), with var. β with C. affinis and C. p. var. virgata treated as synonyms. His diagnosis corresponds with that of Rossmässler for C. p. var. virgata, without paying attention to the difference of the neck keel.
Küster (1850: 52-54, pl. 5, figs. 28-37) also used the name C. bidens, with var. A instead of var. β. In his diagnosis: "Costulata, palato calloso; peristomate continuo, soluto" the difference of the neck keel is not mentioned, too.
A. Schmidt (1868: 107-108) treated C. papillaris and C. virgata with reservation as independent species, because he had received mixed samples of both (indication of a possible sympatry). He distinguished the latter by "den breiter umgeschlagenen oben durchweg lostretenden Mundsaum, die flachen Umgänge, die stärkere Streifung". But he also mentioned "Mittelformen", for example that from Toulon in France.
Paulucci (1878: 13-14) listed for the species named C. bidens the varieties var. circinata, var. virgata = affinis and var. brevissima. The var. circinata was characterized as follows (: 39): "très légèrement strié, ... largement pourvue du bourrelet"; so she assumed for this variety an intermediate position between the type form and the var. virgata. C. b. var. brevissima is a dwarf form from S. E. Sicily sent away under this name by Benoit. Further, she described (: 39) two ribbed species of the group, C. transitans and C. deburghiae, from Calabria. With the latter, which is a form of P. solida, she united (: 14) the ribbed variety of bidens, C. tinei, from Sicily (see Nordsieck 2002: 37).
O. Boettger (1878: 51) subdivided the species, which he, too, named C. bidens, into three subspecies: subsp. bidens (among others with var. circinata), subsp. virgata (among others with var. affinis and the ribbed vars. transitans and deburghiae + tinei, in accordance with Paulucci) and subsp. brevissima. Furthermore, he gave accurate information on the range of the species. A widely ribbed form from Sicily was described by him as an independent species, C. rudicosta.
Westerlund (1901: 137-138) treated Boettger's subspecies, as well as the ribbed forms of P. bidens as species and gave a list of all their varieties described so far.
The work of 19th century malacologists provided a foundation for the subdivision of P. bidens, on which modern researchers could have based their work.

III. Modern work on P. bidens

But this did not happen. In the following modern papers no attempt was made to work out a subdivision of P. bidens which reflects its actual diversity.
Forcart (1965: 122-123), after examination of the samples of P. bidens which were available from southern Italy, stated: P. papillaris „ist ausserordentlich variabel. Zahlreiche Populationen weisen Schaleneigenheiten auf und wurden mit besonderen Namen belegt. Vermutlich beziehen sich die von Westerlund (1901: 137-138) unter den Namen ... angeführten Formen auf Populationen oder auch individuelle Varianten von P. papillaris".
Alzona (1971: 94-95) listed all varieties which, as far as he knew, had been described from Italy, as subspecies of P. bidens and P. affinis without review. In a footnote one of the editors of his paper (: 94, as I assume, Toffoletto) stated: P. affinis "non è probabilmente altro che un insieme di popolazioni, con nicchio robusto, ispessito, e costulatura talora molto evidente, del ciclo variabilissimo di P. bidens, ..."
Giusti (1973: 240-246) regarded all taxa described so far as synonyms of P. papillaris, which he did not divide into subspecies with the following explanation (: 245): "ho potuto constatare come alcune "specie" altro non fossero che forme di passaggio tra una forma e l'altra o tra una forma e le semplice P. papillaris (Müller)". "Ho potuto ... constatare ... la variabilità delle popolazioni ed il loro mutare in rapporto alla esposizione, alla freschezza o aridità del biotopo". And concerning the forms from Sicily and Calabria the following (: 246): "Si tratta indiscutibilmente di demi locali, casualmente distribuiti ed inframezzati da altri demi a loro volta più o meno differenziati, certamente in rapporto solo con determinati fattori ambientali". Neither the intermediate forms are specified, nor the assertion, that the differing forms from Sicily and Calabria were simple modifications, is founded. On the other hand, Giusti (: 237, fig. 28 A, C ) was the first who gave an accurate figure of the genital organs of P. bidens (from Isola Salina).
Manganelli et al. (1995: 25), in the Checklist delle specie della fauna italiana listed P. papillaris without subspecies, with the addition (= affinis = circinata = transitans = virgata).
Giusti et al. (1996: 375-379, figs. 421-427) determined P. bidens from the Maltese Islands as P. papillaris without assigning it to a subspecies and stated (: 379), that "the Maltese populations correspond to the typical morph" (which is not true, because only based on the sculpture, see chapter V). They repeated that C. p. var. virgata and C. affinis should be regarded as "local demes". And: "However, some authors still refer to them as true subspecies, ignoring evidence to the contrary in the literature". This "evidence", however, cannot be found in the literature.
The opinion of Giusti and co-workers on the intraspecific diversity of P. bidens has not been confirmed by my research (chapter V).

IV. Nomenclature of the species

See Nordsieck (2013).

Figs. 1-2. Shell of P. bidens (frontal und body whorl dorsal).
1. P. b. bidens, mainland Italy (different localities); 2. P. b. affinis, Sicily (different localities).
Scale 10 mm.  

Figs. 3-4. Shell of P. b. bidens.
3. Body whorl dorsal (view on lunellar); 4. body whorl frontal (oblique view into aperture, rudimentary principal plica visible).
Abbreviations: aup = anterior upper palatal plica; lu = lunella; plp = posterior lower palatal plica; pr = principal plica or principalis rudiment; su = suturalis (-es). 

V. Subspecies division of P. bidens

Until now, my research of the intraspecific diversity of P. bidens was restricted to shell characters. The material examined is deposited in the collection of the Forschungsinstitut Senckenberg (SMF) and in my own collection. It comes from 182 localities altogether, most of which from Italy, which is assumed to be the centre of origin of the species. The sample numbers from the different regions are the following: Mainland Italy 72, Sicily 39, Malta 4, Tunisia 7, western Mediterranean countries (Sardinia, Corsica, Balearic Islands, S. France, Catalonia) 22, eastern Mediterranean countries (Dinaric countries, Greece, Turkey) 38.
52 samples of P. bidens from mainland Italy, Sicily and Malta were subjected to a more thorough analysis (if available, 10 specimens per sample). The G type lunellar of the species (Nordsieck 2007: 91-93; see fig. 3) is nearly invariable; therefore only the following characters could be used:
Development of
1. white surface layer of the shell;
2. sculpture;
3. neck of body whorl with basal keel;
4. peristome;
5. parallel lamella and spiralis rudiment (with this term not the lamella fulcrans is meant, but the indistinct lamella running forward parallelly to the parallel lamella);
6. inferior lamella;
7. subcolumellar lamella;
8. palatal callus and anterior palatal folds (running from the palatal callus inwards).
It resulted that only the characters 2., 3., 4., 7. and 8. were suitable to define geographical subunits within the species. The most important character is the development of the peristome. By this character, two large subunits = main subspecies are defined: P. b. bidens from mainland Italy as far as N. Calabria and P. b. affinis from Sicily, S. Calabria and Malta (see figs. 1 – 2). In P. b. bidens, the peristome is nearly always attached, in P. b. affinis it is detached. These two subspecies can also be identified in the material from the remaining Mediterranean countries which makes possible the reconstruction of the distribution of the species from Italy into these regions (see map).
As a result of this distribution, intermediate forms have originated by secondary contact. An intermediate form which has already been recognized by A. Schmidt (1868: 107) occurs in Toulon, S. France. I could find a further one, as far as known, restricted to the Penisola Sorrentina and the island of Capri, Campania; it is, simply said, a P. b. bidens with the detached peristome of P. b. affinis. The form from Malta (Nordsieck 2007: pl. 13, fig. 5) is intermediate between P. b. bidens and P. b. affinis in the development of the peristome, but corresponds in other characters with P. b. affinis from S. E. Sicily (circinata).
Besides, P. b. affinis differs from the nominate subspecies by a more strongly developed basal keel (see fig. 1) and a more frequently emerging subcolumellar lamella (in P. b. bidens not visible in front view in ~ 1/4 of the examined specimens, in P. affinis only in ~ 1/20). A further distinguishing character, which was unknown until now, is the presence of a complete principal plica. In a part of the specimens of P. b. bidens the anterior upper palatal fold, running inwards from the palatal callus, is continued by a weak, but well-visible fold which reaches the principalis rudiment above the lunella (figs. 3-4); it is thus recognized as the rudimentary principal plica. In P. b. affinis, such a principal plica could not be observed.
As to the sculpture, most samples of P. b. affinis are more strongly rib-striated (rib density on 2 mm of the penultimate whorl = R2 mean 10-14.5) than those of P. b. bidens (R2 mean 13-19). However, there are exceptions, e. g. the form of P. b. affinis from Siracusa (circinata) and that from Malta, with a sculpture corresponding to that of P. b. bidens (R2 mean 14-17). Ribbed forms (R2 mean 7-8.5) are only present within the main subspecies P. b. affinis. They have been found in S. Sicily and are provisionally united in a subspecies which has to bear the oldest name P. b. tinei. It comprises several geographic forms, which occur in close vicinity of normally sculptured P. b. affinis (e.g. near Sciacca, Caltabellotta, Palazzo Adriano, Agrigento, Modica); in some localities intermediate forms have been found (e.g. near Agrigento). A further ribbed subspecies within the main subspecies P. b. affinis is P. b. transitans from Stilo, S. E. Calabria.
P. b. bidens occurs in mainland Italy, but the question remains where it is really autochthonous. Giusti & Mazzini (1971: 296) stated that P. papillaris "e' specie frequentissima lungo le coste e nell'interno (alle basse quote) di tutta la penisola italiana e nelle isole." From this statement one could be under the impression that P. b. bidens has a natural distribution all over the Italian peninsula. But this is not the case. Nearly all samples of the species which I have collected on the Italian peninsula came from human settlements, while in the natural environs the species was absent. Thus I infer that in the greater part of the peninsula the species was introduced by man. Only in several localities in Puglia east of Ofanto river and some in Basilicata I have collected P. b. bidens in natural habitats (in my judgement nearly not affected by human activities). Further investigations are necessary to find out if these regions are the centre of origin of P. b. bidens.
The result of the research is summarized by the following systematical list:
P. bidens (Linné 1758):
Main subspecies b. bidens:
b. bidens (= papillaris O. F. Müller 1774);
main subspecies b. affinis:
b. affinis (Philippi 1836) (= virgata Rossmässler 1836, = mamertina Benoit 1840, = brevissima L. Pfeiffer 1859, = circinata Paulucci 1878);
b. tinei (Westerlund 1878) (= lanceolata Benoit 1882, = agrigentina Westerlund 1890);
b. transitans (Paulucci 1878);
b. rudicosta (O. Boettger 1878) (little known, possibly subfossil).
P. b. circinata, which I formerly regarded as a subspecies (Nordsieck 2002: 36), is classified with P. b. affinis, because it differs from it only by the sculpture. The var. circinata sensu Paulucci (1878: 39) is double-headed, because it also contains the P. b. bidens from southern mainland Italy with strong palatal callus. As type locality of var. circinata Siracusa, S. E. Sicily, is stated (syntypes SMF).
The affiliation of P. b. transitans with P. solida, which I proposed in a former paper (Nordsieck 2002: 36), was wrong, because, in contrast to that species, it exhibits a dark subsutural band and does not much differ from P. b. affinis occurring nearby.

VI. Distribution of P. bidens in the Mediterranean

The work on the material of P. bidens, which was available from the Mediterranean countries outside of Italy (and Malta), was restricted to the determination of the main subspecies.
The result of this determination is the following:
N. Tunisia: P. b. affinis (= tabarkana Pallary 1927), additionally a ribbed form (P. b. punica Bourguignat 1868);
Sardinia: P. b. affinis (= sulcitana Charpentier 1852);
Corsica: P. b. bidens;
S. France (Provence, Languedoc): P. b. bidens, in Toulon an intermediate form P. b. affinis / bidens;
Balearic Islands: P. b. affinis;
Catalonia: In and near Barcelona P. b. affinis (= catalonica Fagot 1884 = barcinensis Westerlund 1893); in Tarragona P. b. bidens;
Dinaric coastal regions and islands from Istria to S. Albania: P. b. bidens;
Ionic Islands and coast of W. Greece as far as Gulf of Patras and Messenia: P. b. bidens;
E. Greece (Korinthos, Island of Rhodos): P. b. affinis;
Turkey (Istanbul, Bursa): P. b. bidens.
From this distribution I conclude that both main subspecies spread from their centres of origin over the regions of western and eastern Mediterranean (see map). Because in all these regions P. bidens is restricted to anthropogenous habitats near the coast, it is assumed that it has been distributed by man and his shipping traffic. In some coastal regions where P. bidens does not occur or is rare, it is replaced by related species, which possibly have also been distributed by man, P. solida in S. France and Siciliaria gibbula (Rossmässler) in N. Dalmatia.

Map. Spreading of the two main subspecies of P. bidens over the Mediterranean, reconstructed from the occurrences of both subspecies outside of Italy (see text). 


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