Albinaria in Crete

Albinaria in Crete

The subspecies concept in South European Clausiliidae

Comment on Welter-Schultes Albinaria Crete

 

Albinaria species in Crete

Hartmut Nordsieck (IX. 2021)

I. Introduction and species list

All clausiliid species in Crete belong to the genus Albinaria Vest 1867. Though Crete represents only a relatively small part of the distributional range of the genus, its species number (40) amounts to one third of the species number of the whole genus. This means that Albinaria achieves the maximum of its diversity on that island. The fragmented landscape, favourable limestone rock areas in three mountain ranges (Lefka, Idi, Dikti Mountains) with many gorges and adjacent lower areas separated by unfavourable plains, may have played an important role for the diversification of the genus, just as the ecological differentiation into insolated open rock-faces and sheltered rock sites as two main habitats for different species of the genus (Gittenberger 1991). There are no other clausiliid groups which compete with the Albinaria species for these niches. The climatic differences between the northern and the southern parts of the island have certainly caused a further diversification (see part II). Besides, diversity has been increased by endemic species originated on northern peninsulas (Gramvousa, Rodopos, Akrotiri) and small islets, especially in the north of Crete (Pondikonisi Island, Dia Island, Dionisades Islands).

The species are listed as follows (in alphabetical order):

Mainland Crete:

A. amalthea (Westerlund 1878)
A. ariadne Schilthuizen & Gittenberger 1991
A. arthuriana (O. Boettger 1878)
A. byzantina (Charpentier 1852)
A. candida (L. Pfeiffer 1850)
A. christae Wiese 1989
A. corrugata (Bruguière 1792)
A. cretensis (Rossmässler 1836)
A. eburnea (L. Pfeiffer 1854)
A. eikenboomi H. Nordsieck 2019
A. fulvula Flach 1988
A. hippolyti (O. Boettger 1878)
A. idaea (L. Pfeiffer 1850)
A. leonisorum (O. Boettger 1901)
A. li Welter-Schultes 1999
A. loosjesi H. Nordsieck 1977
A. maltzani  (O. Boettger 1883)
A. moreletiana (O. Boettger 1878)
A. praeclara (L. Pfeiffer 1853)
A. rebeli A. J. Wagner 1924
A. sphakiota (Maltzan 1887)
A. spratti (L. Pfeiffer 1846)
A. sturanyi A. J. Wagner 1924
A. sublamellosa (O. Boettger 1883)
A. tenuicostata (L. Pfeiffer 1865)
A. terebra (L. Pfeiffer 1853)
A. teres (Olivier 1801)
A. troglodytes (A. Schmidt 1868)
A. ulrikae Schilthuizen & Gittenberger 1990
A. vexans (O. Boettger 1883)
A. violacea Schilthuizen & Gittenberger 1990
A. virginea (L. Pfeiffer 1846)
A. wiesei Gittenberger 1988
A. xanthostoma (O. Boettger 1883)

Pondikonisi Island:
A. pondika Welter-Schultes 2010

Dia Island:
A. jaeckeli Wiese 1989
A. retusa (Olivier 1801)
A. torticollis (Olivier 1801)

Dionisades Islands:
A. janicollis Schultes & Wiese 1991
A. janisadana Loosjes 1955

After having worked through the revisions of Welter-Schultes (2000, 2010), in which several species have been united with other ones,  I see no reason to change the rank of the species (Nordsieck 2017).
A survey of all known Albinaria taxa from Crete with pictures was given by Kittel & Hirschfelder (2018).
The modifications of the species system of the A. cretensis group resulting from the genome-wide DNA analysis of Bamberger et al. (2021) is discussed in part IV.

II. Shell morphology

  1. Grouping of species

According to shell morphology, the species have been assembled within five groups (Nordsieck 1999):

  1. candida group: A. amalthea, A. arthuriana, A. candida, A. fulvula, A. hippolyti, A. leonisorum, A. loosjesi, A. pondika, A. ulrikae, A. violacea, A. wiesei, A. xanthostoma;
  2. torticollis group: A. christae, A. jaeckeli, A. torticollis;
  3. cretensis group: A. byzantina, A. cretensis, A. eburnea, A. eikenboomi, A. sphakiota, A. sublamellosa, A. tenuicostata, A. troglodytes, A. vexans, A. virginea;
  4. teres group: A. ariadne, A. corrugata, A. idaea, A. janicollis, A. janisadana, A. li, A. maltzani, A. moreletiana, A. praeclara, A. retusa, A. spratti, A. terebra, A. teres;
  5. caerulea group: A. rebeli, A. sturanyi.

The first three groups contain only species endemic for Crete. The fourth group includes additionally to the endemic species from Crete some from Cyclades, Dodecanese and Cyprus. The two species of the fifth group are similar to A. caerulea. They have extremely restricted ranges; possibly they originate from forms which have reached Crete from the Aegean islands.
The proposed groups are based only on shell morphology. The grouping does not claim to present monophyletic groups, as assumed by some authors, because it is clear that there is a certain amount of convergences in shell morphology. Therefore, a ranking of these groups as subgenera, as proposed again in MolluscaBase (2018), is rejected.

  1. Characters of closing apparatus

Like in other Albinaria groups (Nordsieck 1999) species with more plesiomorphic characters of closing apparatus = CA and species with more apomorphic ones can be recognized.
The complete CA of Albinaria is regarded as plesiomorphic (Nordsieck 1997), because it is improbable that its complex palatal system has evolved several times de novo from the reduced one without palatal plicae. It is characterized as follows (Fig. 1): All palatal plicae present, especially anterior upper palatal plica (aupp), anterior lower palatal plica = basalis (bas) and posterior lower palatal plica = subclaustralis (scl); clausilium plate (cp) normally developed (fitted in the frame of lunellar and subcolumellar lamella). In few species even a lowest palatal plica = sulcalis (sul) is present; it must not be confounded with the posterior lower palatal plica.

Fig. 1. Characters of CA, example Albinaria ulrikae, GR, Crete, near Rodia, ex N. Body whorl, oblique view into aperture and view on lunellar. Shell height 22.1 mm.
Abbreviations: aupp = anterior upper palatal plica, bas = anterior lower palatal plica = basalis, cp = clausilium plate, il = inferior lamella, lu = lunella, pr = principal plica, scl = subclaustralis, sl = superior lamella, sp = spiral lamella, sul = sulcalis, upp = (posterior) upper palatal plica.

If one compares the Albinaria species from Crete, species with all states from most plesiomorphic CA to most apomorphic one are present (Figs. 2-5). Especially the recognition of species with plesiomorphic CA may be of interest for the reconstruction of the phylogeny of Albinaria on Crete. 11 from 40 species, i. e. about a fourth of the species, exhibit a more plesiomorphic CA. These are the following (in alphabetical order, with range information, abbreviations see text):

A. amalthea, N. W. Crete: aupp and bas present;
A. ariadne, N. W. central Crete: bas present;
A. arthuriana, N. E. central Crete: aupp and bas present, even sul;
A. candida, N. W. Crete: aupp and bas present, aupp in part reduced;
A. fulvula, S. E. central Crete (Fig. 4): bas present;
A. hippolyti (aphrodite O. Boettger), N. W. central Crete: aupp and bas present;
A. hippolyti (hippolyti, holtzi Sturany), N. W. central Crete: bas present;
A. loosjesi, N. W. Crete: aupp present, bas reduced;
A. pondika, Pondikonisi island (N. W. Crete): aupp and bas present;
A. ulrikae (Fig. 2), A. violacea, N. W. central Crete: aupp (in part two) and bas present, even sul;
A. wiesei, N. W. eastern Crete (Fig. 3): aupp and bas present;
A. xanthostoma, N. W. Crete: bas present.

According to the degree of reduction, the Cretan species are ordered as follows:

  1. A. arthuriana, A. ulrikae (Fig. 2), A. violacea: even sul present;
  2. A. amalthea, A. h. aphrodite, A. pondika, A. wiesei (Fig. 3): aupp and bas present; also A. candida, but aupp in part reduced, and A. loosjesi, but bas reduced;
  3. A. fulvula (Fig. 4), A. h. hippolyti, A. h. holtzi, A. xanthostoma: bas present;
  4. A. leonisorum, A. sublamellosa, A. eikenboomi, A. troglodytes: bas in part or rudimentary present;
  5. remaining species (e. g., A. idaea Fig. 5): named palatal plicae absent.

Figs. 2-5. Albinaria species in Crete. Frontal, body whorl with view on lunellar and oblique view into aperture. Shell height = H (mm).
1. A. ulrikae, CA much plesiomorphic, GR, Crete, near Rodia, ex N; H 22.1.
2. A. wiesei, CA less plesiomorphic, GR, Crete, Selinari church near Neapoli, paratype, ex NNM 56084; H 16.85.
3. A. fulvula, CA more apomorphic, GR, Crete, N. of Anatoli, paratype, ex NNM 56092; H 17.1.
4. A. idaea amabilis, CA much apomorphic, GR, Crete, Kedros Mountains, paratype, ex NNM 56824; H 16.9.

A further important character of the CA is the position of the lunellar. In most species taxa the lunellar is dorsally to dorsolaterally situated. In some taxa, however, it is in deeper position, lateral or deeper. These are the following: A. amalthea (amalthea), A. hippolyti (asterousea Schilthuizen, Welter-Schultes & Wiese), A. leonisorum, A. sphakiota, A. troglodytes (interpres Westerlund), A. violacea (dextrogyra Schilthuizen & Gittenberger). An extreme case is A. jaeckeli, in which the lunellar is in ventral position. Like in other clausiliids, the change to a deeper position of the lunellar is regarded as a better protection against evaporation. It is interesting that – except for A. jaeckeli – all taxa with deeply situated lunellar belong to the groups with plesiomorphic CA (groups 1 – 4). In the taxa with apomorphic CA (group 5) the lunellar is nearly invariable. Protection against desiccation is achieved by the secretion of an epiphragma in aestivation. According to my experience species with much plesiomorphic CA do not secrete such epiphragmas.

It is striking that the species with the most plesiomorphic CA (group 1) have also the plesiomorphic character white surface layer of the shell absent (Fig. 2). In several species with plesiomorphic CA the inferior lamella is high; like in other Alopiinae this is also regarded as a plesiomorphic character (Figs. 2-3).

If one compares the ranges of the Cretan Albinaria species it results that all species with plesiomorphic CA (except of A. fulvula) are distributed in the northern part of Crete or on northwestern islets. The reason may be that these parts of Crete have not so extreme climatic conditions than the other parts of the island (southern part, mountains, other islets).

  1. Character protoconch sculpture

The position of the beginning of the protoconch sculpture has revealed to be an important character for the definition of species taxa in Crete (Nordsieck 2017) (Figs. 6-7). Three groups (I-III) containing the following taxa are recognized.

I (ribbing begins in the course of the first whorl): A. idaea (rolli group), A. janicollis, A. teres (manselli O. Boettger), A. praeclara (praeclara group), A. virginea (rodakinensis Wiese), A. terebra;

II (ribbing begins at about the beginning of the second whorl): A. ariadne, A. idaea (remaining subspecies), A. maltzani, A. praeclara (parallelifera group).

III (ribbing begins in the course of the second whorl or near to its end): remaining species or subspecies.

In A. praeclara and A. idaea subspecies of groups I and II are included. The latter is an especially interesting case, because the differences of this character within the species have not been noticed until now. Engelhard & Slik (1994) gave a number of unribbed apical whorls (1-2.6), which, however, is higher than that of the first smooth part of the protoconch. Nordsieck (1998) stated that ribbing always begins with the second whorl, also not correct. Welter-Schultes (2000, 2010) studied only number and prominence of the ribs of the second whorl, not the position of their first appearance. In this respect, A. i. rolli and the two subspecies from the Paximadia Islands belong to group I, the remaining subspecies to group II (Nordsieck 2017: 17).

Figs. 6-7. Protoconch of Albinaria species (from above).
6. Protoconch (scheme): 1= ending of first whorl, 2. = of second whorl. I – III = groups with different position of the beginning of protoconch sculpture: Group I = in the course of the first whorl. Group II = at about the beginning of the second whorl. Group III = in the course of the second whorl or near to its end.
7. SEM-photos of the protoconch of Albinaria species, ex SMF. Scale 300 μm. Group I: A. terebra, GR, Crete, Kefali Peninsula near Kali Limenes. Group II: A. i. idaea, GR, Crete, Idi Mountains between Kamares and Lochria. Group III: A. corrugata inflata, GR, Crete, Knossos near Iraklion.

III. Genital morphology

With regard to the species number in the past the genitalia of only few Albinaria species from Crete have been examined.
A. J. Wagner (1924, 1925) gave short descriptions of the genitalia of eight species (A. arthuriana, A. corrugata, A. aphrodite = A. hippolyti, A. rebeli, A. cretensis = A. sphakiota, A. sturanyi, A. sublamellosa, A. virginea). In the course of their work on hybrid zones in A. hippolyti, Schilthuizen & Lombaerts in Schilthuizen (1994) examined the genitalia of some subspecies of that species. My own work until now is restricted to 14 species, mainly of the A. cretensis group (A. amalthea, A. byzantina, A. candida, A. corrugata, A. cretensis, A. eburnea, A. praeclara, A. sphakiota, A. sublamellosa, A. tenuicostata, A. teres, A. troglodytes, A. virginea, A. xanthostoma). The presence / absence of the penial caecum and the length relations of the parts are of importance for characterizing species. A grouping of the species based on genital morphology, however, was not possible until now.
A comparison of the species of the A. cretensis group is of special interest, because the species system within this group is controversial (see Welter-Schultes 2000, 2010).
In the past four species of the group have been examined: A. virginea, A. sphakiota (A. J. Wagner 1924: 10, 13); A. sublamellosa (A. J. Wagner 1925: 59, fig. 113), and A. mitylena = A. byzantina (Fuchs & Käufel 1934: 78, fig. 7). The description of A. virginea of Wagner is in contrast to my results (see below), because it is said to have a penial caecum and a biramous penial retractor. Perhaps, another species is concerned. A. sublamellosa is classified by Wagner with Delima (as type species of a subgenus Priodelima), because the penial caecum is absent.
The examination of eight species of the cretensis group and three species of the candida group from the same region (A. candida, A. amalthea, A. xanthostoma)  has revealed considerable differences mainly in the male copulatory organs, which are useful for species delimitation. For comparison also some species from eastern Crete have been examined (A. corrugata, A. teres, A. praeclara).
The result is that the species of the A. cretensis group differ by the presence of a penial caecum or instead a penial papilla and in the length relations of the copulatory organs. Two groups of species could be recognized, those with penial caecum and penis of normal length (A. tenuicostata, A. eburnea, A. cretensis, A. sphakiota) and those with penial papilla and shortened penis (A. troglodytes, A. virginea, A. sublamellosa). The characters of the first group are regarded as plesiomorphic, because they are shared by many other Albinaria species and other genera of the Alopiini. A. byzantina has an intermediary position, because it exhibits a reduced penial caecum and a shortened penis.
The differences between the species, which have been assembled by Welter-Schultes (2010) within the megaspecies A. “cretensis”, are of special interest. A. byzantina, A. troglodytes and A. virginea have a short penis, in A. cretensis it is of normal length. A. byzantina has a short vagina (dpb/v 1.6) and a reduced penial caecum (which forms a small loop), the epiphallus is especially long (ep/p >3). In A. troglodytes and A. virginea , in which instead of a penial caecum a penial papilla is present, the epiphallus has a normal length (ep/p ≤3). A. cretensis has a fully developed penial caecum and an epiphallus of normal length. All four species have an undivided penial retractor (in A. cretensis penial branch reduced). Thus, A. “cretensis” includes species which are rather different; it is certainly no monophyletic unit.
A. sublamellosa is like A. troglodytes and A. virginea.
A. sphakiota is like A. cretensis, with biramous penial retractor, penial branch weakened.
A. tenuicostata has a biramous penial retractor and a fully developed penial caecum which is relatively longer than in the other species.
A. „tenuicostata“ from Paleochora (fortress) has been wrongly determined, because it is like A. troglodytes and A. virginea.
A. eburnea is similar to A. cretensis, because it has epiphallus and penis of normal length and a fully developed penial caecum. The penial retractor is biramous to undivided. All characters are in contrast to A. byzantina with which it has been united by Bamberger et al. (2021). Therefore, it remains here to be regarded as a species of its own.
As concerns the species of the candida group from the same region, the result is as follows:  A. candida is like A. troglodytes and A. virginea (penis shortened, with penial papilla instead of penial caecum). A. amalthea and A. xanthostoma are similar to A. tenuicostata (penis of normal length, with well-developed penial caecum). The taxon from Cape Spada, determined as A. tenuicostata subsp. (Nordsieck 2017: 13), is more similar to A. xanthostoma and therefore classified with that species. The candida group species, which exhibit a more or less complete, i. e. plesiomorphic CA (see part II), are obviously not closely related.
The three examined species from eastern Crete do not much differ; they all have an epiphallus and penis of normal length, a penial caecum and a more or less biramous penial retractor. A. corrugata and A. teres are similar; A, praeclara exhibits a relatively longer vagina and a shorter proximal part of epiphallus.

IV. Allozyme and DNA analyses

The results of different allozyme and DNA analyses are not consistent with shell morphology; compared with one another, they yield different groupings of species.

Allozyme analysis:

Schilthuizen & Gittenberger 1996:

A. corrugata, A. moreletiana;
A. sublamellosa;
A. idaea, A. terebra;
A. arthuriana, A. spratti, A. hippolyti, A. cretensis (= A. virginea), A. christae.
This grouping is in contrast to the close relationship of A. sublamellosa and A. virginea (see part III).

DNA analyses:

Douris et al. 1998:

A. terebra;
A. xanthostoma;
A. eburnea, A. cretensis (= A. virginea), A. violacea, A. spratti, A. ulrikae, A. hippolyti, A. corrugata;
A. praeclara, A. maltzani, A. moreletiana?;
A. torticollis, A. jaeckeli, A. teres, A. retusa?.

Van Moorsel, van Nes, Gittenberger & Megens in Van Moorsel 2001:

A. torticollis;
A. teres;
A. candida, A. cretensis (= A. virginea), A. ulrikae;
A. corrugata, A. leonisorum, A. wiesei;
A. spratti.

Van Moorsel, Schilthuizen & Gittenberger in Van Moorsel 2001:

Only well-supported groups are given:
A. ulrikae, A. spratti, A. praeclara, A. torticollis, A. cretensis (= A. virginea);
A. teres, A. corrugata.

Schilthuizen et al. 2004:

A. hippolyti, A. candida, A. cretensis (= A. virginea), A. ulrikae, A. torticollis, A. spratti;
A. arthuriana, A. wiesei, A. teres, A. corrugata.

Dimopoulou et al. 2017:

A. tenuicostata;
A. moreletiana, A. praeclara, A. arthuriana;
A. corrugata, A. wiesei, A. violacea, A. spratti, A. ulrikae, A. hippolyti, A. eburnea, A. sphakiota, A. ariadne, A. cretensis (= A. virginea);
A. teres, A. sturanyi;
A. retusa, A. torticollis, A. jaeckeli.
This grouping is in contrast to the close relationship of A. tenuicostata and the other included species of the cretensis group (see part III).

Not considering the species of Dia Island a western and an eastern group are recognizable, but there are overlappings.
Western group: A. candida, A. cretensis (= A. virginea), A. eburnea, A. hippolyti, A. spratti, A. ulrikae, A. violacea.
Eastern group: A. arthuriana, A. corrugata, A. maltzani, A. moreletiana, A. praeclara, A. teres, A. wiesei.
It is evident that the results of DNA analyses mirror the distribution of the species better than their morphological similarity.The conclusion, however, that morphology does not reflect the relationships of the species is premature. Introgression caused by hybridization, which is frequent in Albinaria  also from Crete, might have influenced the group affiliations. The hitherto presented analyses are not yet suited to serve as a basis for a classification of the Cretan Albinaria species.

Bamberger et al. 2021:

The authors present a DNA analysis of the A. cretensis group based on genome-wide ddRAD sequences. The aim of the paper is the evaluation of some methods for species delimitation. The topology of the resulting tree is as follows (fig. 2):
A. tenuicostata is basal to the other species.
The form from Agia Irini (= A. sp. 1), until now included in A. tenuicostata (Nordsieck 2017: 17, fig. 14),  is within A. tenuicostata the sister group of the majority of the A. tenuicostata samples.
A. byzantina is basal to the remaining species.
A. eburnea is basal to the rest of the remaining species.
The rest of the species forms two clades: A. sublamellosa and A. cretensis group sensu stricto + A. virginea group.
A. sublamellosa includes the type form of A. troglodytes vexans, because this taxon has a sublamellosa genome, admixed with genes of other species. It is regarded here as species of its own, because it differs from A. sublamellosa in shell shape and sculpture and a more deeply situated closing apparatus and occurs sympatrically with it in the Samaria gorge, with few transitional specimens (named until now A. s. heteroptyx).
The other clade includes the A. cretensis group sensu stricto (A. cretensis, A. sphakiota) and the A. virginea group (A. virginea, A. troglodytes) as sister groups.
Within the A. virginea group clade the other form of former A. troglodytes vexans (A. troglodytes interpres) is basal.
Two samples of western A. virginea (= A. sp. 2) are basal to the remaining samples of the group.
Within the remaining A. virginea group – except of the hybrid form from Kournas which comes out basal to A. virgineaA. virginea and A. troglodytes are sister groups.
The former contains A. rodakinensis, because of its ribbed protoconch formerly regarded as species of its own, the latter the third included sample of western A. virginea.
The species of the megaspecies A. “cretensis” appear in two different clades, A. byzantina clade and clade of A. cretensis group sensu stricto + A. virginea group. Thus, like in genital morphology that taxon reveals as non-monophyletic.
As result of their species delimitation method, Bamberger et al. regard the taxa called A. sp. 1 and A. sp. 2 as species, while A. byzantina and A. eburnea are united to one species. The other clades are evaluated as species; within the A. cretensis group sensu stricto A. cretensis and A. sphakiota are separated as species.
The authors have only considered shell morphology for their work. If one compares the results of the genome-wide analysis with those of the genital examination (part III), the following is stated:
A. tenuicostata has the plesiomorphic type of male copulatory organs (penial caecum present, penis of normal length).
A. byzantina has apomorphic male copulatory organs (penial caecum reduced to a loop, penis shortened, epiphallus lengthened).
A. eburnea and the A. cretensis group sensu stricto have the plesiomorphic type of male copulatory ogans like A. tenuicostata, but with shorter caecum.
A. sublamellosa and the A. virginea group have the apomorphic type of male copulatory organs (penial papilla instead of penial caecum present, penis shortened) in common.
The western A. virginea (= A. sp. 2, including the wrongly determined A. „tenuicostata“ from Paleochora) is like the A. virginea group.
Because of their different genital morphology, the union of A. byzantina and A. eburnea within one species is not supported; therefore, both taxa are proposed to be regarded as species of their own.

References

Bamberger, S., Xu, J. & Hausdorf, B. (2021): Evaluating species delimitation methods in radiations: the land snail Albinaria cretensis complex on Crete. – Systematic Biology: 65 pp.

Dimopoulou, A., Antoniou, A., Mylonas, M., Vardinoyiannis, K. & Poulakakis, N. (2017): Inferring phylogenetic patterns of land snails of the genus Albinaria on the island of Dia (Crete, Greece). – Systematics and Biodiversity, 15 (5): 1-13.

Douris, V., Cameron, R. A. D., Rodakis, G. C. & Lecanidou, R. (1998): Mitochondrial phylogeography of the land snail Albinaria in Crete: long-term geological and short-term vicariance effects. – Evolution, 52: 116-125.

Engelhard, G. H. & Slik, J. W. F. (1994): On altitude dependent characters in Albinaria idaea (L. Pfeiffer, 1849), with a revision of the species (Gastropoda Pulmonata: Clausiliidae). – Zoologische Mededelingen, 68 (3): 21-38.

Fuchs, A. & Käufel, F. (1934): IV. Land- und Süßwassermollusken aus Griechenland und von den Inseln des Ägäischen Meeres. – In: F. Werner: Ergebnisse einer zoologischen Studien- und Sammelreise nach Griechenland, namentlich nach den Inseln des Ägäischen Meeres: 71-90, 3 pls.

Gittenberger, E. (1991): What about non-adaptive radiation? – Biological Journal of the Linnean Society, 43: 263-272.

Kittel, K. & Hirschfelder, H.-J. (2018): The genus Albinaria Vest 1867 in Crete – a comprehensive and updated survey of all known taxa (Gastropoda: Pulmonata: Clausiliidae). – Acta Conchyliorum, 17: 1-228.

MolluscaBase (2018): Clausiliidae Gray, 1855. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=833936

Nordsieck, H. (1997): Phylogeny of and within the AlbinariaIsabellaria group (Gastropoda: Pulmonata: Clausiliidae). – Heldia, 4, Sonderheft 5: 53-61.

Nordsieck, H. (1998): A new subspecies of Albinaria idaea (L. Pfeiffer 1850) (Gastropoda: Stylommatophora: Clausiliidae). – Heldia, 2 (5/6): 123-126, pl. 17.

Nordsieck, H. (1999): Annotated check-list of the species of the AlbinariaIsabellaria group (Gastropoda: Stylommatophora: Clausiliidae). – Mitteilungen der deutschen malakozoologischen Gesellschaft, 62/63: 1-21.

Nordsieck, H. (2017): New species taxa of the genus Albinaria Vest (Gastropoda, Stylommatophora, Clausiliidae) in Crete. – Conchylia, 48 (1-2): 9-30, 5 pls.

Schilthuizen, M. (1994): Differentiation and hybridisation in a polytypic snail. – Thesis, Leiden University: 178 pp..

Schilthuizen, M. & Gittenberger, E. (1996): Allozyme variation in some Cretan Albinaria (Gastropoda): paraphyletic species as natural phenomena. – In: Taylor, J. (ed.): Origin and evolutionary radiation of the Mollusca: 301-311. Oxford.

Schilthuizen, M., Gutteling, E., Van Moorsel, C. H. M., Welter-Schultes, F. W., Haase, M. & Gittenberger, E. (2004): Phylogeography of the land snail Albinaria hippolyti (Pulmonata: Clausiliidae) from Crete, inferred from ITS-1 sequences. – Biological Journal of the Linnean Society, 83: 317-326.

Van Moorsel, C. H. M. (2001): Molecular phylogenetics of a speciose group: Albinaria and the search for homology. – Thesis, Leiden University: 120 pp.

Wagner, A. J. (1924): Ergänzungen und Erläuterungen zur Systematik der Clausiliiden. II. Neue Formen und Arten des Genus Albinaria ex rect. mea (Schluss). – Annales Zoologici Musei Polonici Historiae Naturalis, 2: 9-23.

Wagner, A. J. (1925): Studien über die Systematik, Stammesgeschichte und geographische Verbreitung des Genus Delima (Hartmann) A. J. Wagner. – Annales Zoologici Musei Polonici Historiae Naturalis, 4: 1-73, 16 pls.

Welter-Schultes, F. W. (2000): Approaching the genus Albinaria in Crete from an evolutionary point of view (Pulmonata: Clausiliidae). – Schriften zur  Malakozoologie, 16: 1-208.

Welter-Schultes, F. W. (2010): Revision of the genus Albinaria in Crete (Greece): presence of geographically variable monotypic and polytypic species (Gastropoda: Clausiliidae). – Archiv für Molluskenkunde, 139: 143-245.