412 species-group names (including 11 replacement names), and 14 genus-group names of the Alycaeidae have been introduced to date. Type materials of 85% (336) of the known species and subspecies were examined, a further 5% (19) of the taxa were studied using available non-type material, and for another 6% (22) the original descriptions were sufficiently detailed to evaluate their taxonomic status. Only 3% of the taxa (12) could not be examined. Special attention was paid to the sculpture of the embryonic whorls and the sutural tube-microtunnel system in order to provide a novel classification for this group.

In this study 363 taxa (320 species or 43 subspecies) are accepted within the family Alycaeidae. Of these, 22 have been described by the lead author and his coauthors in previous publications. In addition, there are 18 species that were formerly classified in Cycloryx and now belong to Pincerna due to its synonymy with Cycloryx. Among the remaining 323 species, 209 (65%) are transferred here to another genus, whilst 114 (35%) have remained in their original genus.

Seven genera are accepted. While some questions (e.g., the distinction between Pincerna and Alycaeus) remained unanswered, this revision made three main achievements: (1) The Dicharax species were identified based on the absence of spiral striation on the entire shell; (2) the Metalycaeus species were identified based on the spiral striation of the protoconch; (3) and Stomacosmethis was separated from Alycaeus based on the extremely short sutural tube.

Five nominal species are being synonymised with other species, and eight species are now treated as subspecies. The following replacement names are proposed: Dioryx urnula niosiensis Páll-Gergely, nom. nov. for Alycaeus urnula var. daflaensis Godwin-Austen, 1914; Dioryx urnula rotundus Páll-Gergely, nom. nov. for Alycaeus urnula var. globosus Godwin-Austen, 1914; Pincerna crenilabris juttingae Páll-Gergely, nom. nov. for Alycaeus crenilabris laevis van Benthem Jutting, 1959; Pincerna crenilabris korintjiensis Páll-Gergely, nom. nov. for Alycaeus crenilabris latecostatus van Benthem Jutting, 1959; Dicharax conicus jatingaensis Páll-Gergely, nom. nov. for Alycaeus conicus var. nanus Godwin-Austen, 1914; Metalycaeus godwinausteni Páll-Gergely, nom. nov. for Alycaeus neglectus Godwin-Austen, 1914; and finally Metalycaeus suhajdai Páll-Gergely, nom. nov. for Alycaeus varius Godwin-Austen, 1914.

land snail, museum collections, systematics, taxonomy

The Alycaeidae are operculate land snails in the superfamily Cyclophoroidea. Approximately 360 Asian species and subspecies have been described so far, and classified into 14 genera or subgenera. Alycaeids inhabit a vast area that stretches from the Western Ghats (India) through the Himalaya to Japan in the east, the Chinese Gansu and Shaanxi provinces in the north and Indonesia to the south (Godwin-Austen 1882–1920; Gude 1921; van Benthem Jutting 1948, 1959; Minato 1988; Gittenberger et al. 2017; Aravind & Páll-Gergely 2019). The alycaeid shell is characterised by a tube, which is closed at its outer end, and opens into the inside of the shell just behind the operculum. This tube is in contact with numerous, extremely narrow tunnels, which are formed by the outermost shell layer (Páll-Gergely et al. 2016).

Some terrestrial caenogastropod genera lacking such a sutural tube have provisionally been assigned to the Alycaeidae. Laotia Saurin, 1953, which includes two species, has been included either in the Diplommatinidae, because of its similarity with Helicomorpha, or in the Alycaeidae, because of its resemblance to the alycaeid Chamalycaeus (Saurin 1953; Páll-Gergely 2014). The latest publication on Laotia placed this genus in Alycaeidae (Do et al. 2015). The Madagascan endemic Boucardicus Fischer-Piette & Bedoucha, 1965 (Madecataulus Fischer-Piette & Bedoucha, 1965 is a synonym, see Emberton and Pearce 1999) has also been placed in Alycaeidae due to a similar shell shape and radula (Emberton 2002; Egorov 2019). Following recent extensive surveys, there are now approximately 200 accepted Boucardicus species (Fischer-Piette et al. 1993; Emberton and Pearce 1999; Emberton 2002; Emberton et al. 2010; Balashov and Griffiths 2015).

Our study covers the systematics of the Alycaeidae sensu stricto, a group that is characterised by the possession of an external tube that runs along the suture (see above). Although anatomical and radular characters are known for some species (Godwin-Austen 1882–1920; Tielecke 1940; Venmans 1956; Emberton and Pearce 1999; Emberton 2001), those can only be used as supplementary information to hypothesise about the relatedness of the genera, and cannot be used for the appropriate generic placement of species at the current time. Thus, the classification presented here is primarily based on morphological characters of the shell.

The current generic subdivision of the Alycaeidae was established over a century ago and no genus-level revision has been proposed since the publication of Kobelt’s (1902) monograph. Arguably, most authors did not examine the type species of genera, especially those of Alycaeus, Chamalycaeus and Dicharax, when attributing new alycaeid species to any of these genera. Moreover, some allegedly diagnostic characters of the genera and subgenera may not reflect evolutionary relationships because these character states have probably evolved in convergence. For example, the low spire was regarded as the key trait of Chamalycaeus (Kobelt 1902). However, most Chamalycaeus, Metalycaeus and Dicharax species are low-spired, and even Alycaeus jousseaumei has a depressed shell, while, there are Dicharax and Metalycaeus species that are high spired (Páll-Gergely et al. 2017). Similarly, Dicharax was defined on the basis of a swelling behind the peristome (Kobelt 1902). This trait, however, occurs in several species of the genera Metalycaeus and Dicharax, and the strength of the swelling is very variable across Dicharax and Metalycaeus species (Páll-Gergely et al. 2017). Lastly, the outer surface traits of the operculum, which defined the genera Pincerna, Stomacosmethis and Metalycaeus, are also variable within species, and, on the other hand, show similar morphology between species not closely related.

The aim of this study is to provide an updated generic classification of the Alycaeidae based on the principles of our former paper (Páll-Gergely et al. 2017) focusing on two key traits largely neglected in previous publications, because these are presumed to be more useful to distinguish natural groups. Firstly, the sculpture on the outer shell surface and secondly, the length and sculpture of the area where the sutural tube is situated and the surface is differently ribbed from the other whorl range. Microtunnels functioning as complex gas exchange device are present with the sutural tube, which could provide useful traits for alycaeid systematics, at least in some of the groups (Páll-Gergely et al. 2016).

Pfeiffer (1858) divided the fourteen species of the genus Alycaeus (equivalent to present-day Alycaeidae) known at the time into two informal groups, namely a species with subturbinate shells (“Subturbinati”) and those with depressed shells (“Depressi”). Benson (1859) named three sections within Alycaeus as follows. (1) Alycaeus: “the last whorl constricted somewhat remotely from the aperture, tumid on both sides of the constriction”; (2) Charax: “constriction broad, contiguous to the aperture, and divided more or less remotely from it, across the whorl, by a ridge which is hollow internally”; (3) Dioryx: “constriction narrow, and immediately behind the aperture; the sutural tube arising proportionally nearer to the peristome than in Alycaeus and Charax”. In Benson’s (1859) system, all the three groups were further sub-divided into unnamed subgroups on the basis of shell shape (Alycaeus and Dioryx) and the morphology of the swelling between the constriction and the aperture (Charax). Pfeiffer (1876) introduced the name Orthalycaeus as a subgenus of Alycaeus and divided it into four subgroups. The name was established without description, but contained 26 species, which made it available. Pfeiffer seemingly intended this name to be used as what we would call today a nominotypical subgenus. He did not select a type species, which was subsequently done by Kobelt (1879: 191), who selected Alycaeus gibbus as the type species of Orthalycaeus. Because this species is also the type species of Alycaeus (also by subsequent designation), these two genus names are objective synonyms. Kobelt and Möllendorff (1897) recognised two genera within the family Alycaeidae: Dioryx and Alycaeus (with the subgenera Orthalycaeus, Chamalycaeus, Charax). Kobelt’s (1902) monograph was based on the same system as the one by Kobelt and Möllendorff (1897), but he treated the Alycaeinae as a subfamily of the Cyclophoridae. Kobelt (1902) recognised Dioryx as a distinct genus and subdivided Alycaeus into four ‘sections’: Alycaeus, Chamalycaeus Kobelt & Möllendorff, 1897 (incorrect attribution of authors, see under Chamalycaeus), Dicharax Kobelt & Möllendorff, 1900 (replacement name for Charax Benson, 1859, non Charax Scopoli, 1777 [Pisces]) and Metalycaeus Pilsbry, 1900. Metalycaeus was described for two Japanese species (A. melanopoma and A. hirasei). Later, A. tsushimanus was also included in Metalycaeus (Pilsbry & Y. Hirase, 1909a). Metalycaeus has only been reported from Japan, and was diagnosed on the basis of a thickened ring on the outer side of the operculum. In later publications it was not accepted as a distinct taxon, but treated as a junior synonym of Chamalycaeus (see Minato 1988). Preston (1907) described the subgenus Pincerna for Alycaeus (Pincerna) liratula Preston, 1907. According to Preston Pincerna has an alycaeiform shell, which is higher than wide, and the operculum with a “circular cup” on its outer surface. The subgenera Cycloryx and Raptomphalus were described by Godwin-Austen (1914). The former is characterised by the ovate-conoid shell and an extremely short tube, which is often pear or club-shaped, whereas the latter has a conspicuous keel on the umbilical margin. Stomacosmethis Bollinger, 1918 was defined on the basis of a pipe, tongue or cup-shaped structure on the outer side of the operculum and included two species from southern Celebes and eastern Borneo. Three genus-group taxa (Sigmacharax Kuroda, 1943, Cipangocharax Kuroda, 1943, Awalycaeus Kuroda, 1951) were described from Japan. These have been used either as genera or as subgenera of Chamalycaeus and can be distinguished from each other as follows: Sigmacharax has a peculiar, sigmoid last whorl with an ovate aperture having an interior ridge, Cipangocharax has a thick, “shelly” operculum with closely imbedded spiral cuticular lamellae on its outer surface, and Awalycaeus has a very short distance between the starting point of the tube and the peristome, its operculum is situated at the aperture, not deeper as in other groups.

In our own works we have defined Metalycaeus by the presence of a spirally striated protoconch, and several species from China, Vietnam, Laos, and Japan have been placed in this genus (Páll-Gergely and Asami 2017; Páll-Gergely et al. 2017). We also found that Chamalycaeus possesses a protoconch without spiral striae, and a teleoconch with spiral striation. Consequently, most species previously classified as Chamalycaeus have been transferred to Metalycaeus or Dicharax. The latter is characterised by the absence of spiral striation on the entire shell (Páll-Gergely et al. 2017). We further synonymised Cycloryx with Pincerna, which is accepted as a distinct genus (Páll-Gergely 2017).

Specimens (shells and radulae) were examined using a low vacuum SEM (Miniscope TM-1000, Hitachi High-Technologies, Tokyo) directly without coating. The ethanol-preserved specimens were dissected under a Zeiss stereomicroscope, and photographs were taken using a Keyence LHX5000 digital microscope.

Photographs of shells were taken using various photographic equipment in our laboratories and in museum collections. Photographs of types deposited in the IZCAS, ZSI, SMF are published here. In cases of the other museums the photographs of types are mostly available online, or they will be published by us in separate papers.

Locality data cited as verbatim from the specimen labels, and no English translations are provided in most cases.

Differences in size are indicated in the generic diagnosis using the following terms: very small (smaller than 3 mm), small (3–4 mm), medium-sized (4–6 mm), large (6–8 mm), very large (larger than 8 mm). We distinguish three regions of the teleoconch, following Páll-Gergely et al. (2017): Region 1 (R1) ranging from the beginning of the teleoconch to the beginning of the differently ribbed region where the sutural tube lies, Region 2 (R2) extending from the end of R1 to the constriction (i.e., the length of R2 usually corresponds with the length of the sutural tube, see Páll-Gergely et al. 2016; Páll-Gergely and Asami 2017), and Region 3 (R3) ranging from the constriction up to the peristome.

In order to maintain consistency with the editorial conventions of MolluscaBase (2020), initials of first names of authors are indicated in all cases where a given author shares the same family name with another malacologist (i.e., Y. Hirase, L. Pfeiffer).

Of the 14 nominal genus-group taxa that have been described (Table 2), we accept seven. The classification proposed in this study is based on unique character states (Dicharax, Dioryx, Metalycaeus) and on unique combinations of character states (other genera) (Table 3). The number of accepted species-level taxa is: Alycaeus: 7, Chamalycaeus: 26, Dicharax: 164, Dioryx: 30, Metalycaeus: 61, Pincerna: 37, Stomacosmethis: 37.

Besides taxonomic problems at the species level (see under Annotated list of species group taxa), some aspects of grouping species into genera turned out to be especially challenging. As a result, the generic boundaries are not completely clear. This may be due to repeated evolution of morphological traits and the presence of the large numbers of species in the genera. In the absence of phylogenetic analyses, the current classification is tentative. We anticipate that some adjustments are inevitable as our understanding of the evolutionary history of this family improves. Some remarks about the species boundaries (numbers correspond with Fig. 5):

(1) Metalycaeus is characterised by the presence of spirally striated protoconch. However, in rare cases the striation is strongly reduced (see M. laevis).

(2) Dicharax is characterised by the absence of spiral striation on both the protoconch and teleoconch. However, striation is present in a few Dicharax species (see remarks under D. candrakirana, and D. depressus). Striae are not elevated threads but are probably a part of the inner shell layers; this structure would not be homologous with the striae present in the other genera. Dicharax is a diverse genus containing 166 species and subspecies. However, meaningful subdivision is not possible at present.

(3) Dioryx and Alycaeus are clearly separated based on the presence of R3, globular shape and weak sculpture of Dioryx. Although the R3 in Alycaeus conformis renders its shell somewhat similar to the shell of Dioryx species, we consider Dioryx to be a recognisable group, which would be monophyletic.

(4) Distinction between Alycaeus and Pincerna is probably the most problematic issue in the system presented here. The genus Cycloryx (treated as a synonym of Pincerna) originally contained species with a very small shell, which has elevated spire usually with strong ribs and very short tube, and taxa from the Himalaya region and northern Myanmar. However, similar species are disjunctly found from Sumatra (Pincerna yanseni), northern Vietnam (A. costulosus) and Borneo (A. globosus). For example, the shell of P. yanseni is hardly distinguishable from that of Hymalayan taxa. The shells of Pincerna liratula and P. thieroti in the Malay Peninsula may be larger than typical Cycloryx, and their sutural tubes may be longer than the extremely short tube of Cycloryx. These two species, however, seem to belong to the same group as Cycloryx according to their strong ribbing, generally short tube and high spire. Furthermore, A. vanbuensis and A. costulosus both of which occur in northern Vietnam, are only distinguishable in tube length. The former is similar to the type species of Pincerna, and the latter to Himalayan species of Cycloryx. Recognition of Pincerna and Cycloryx as different genera requires to classify A. vanbuensis and A. costulosus into those genera on the basis of the tube length, which would not be acceptable. For these reasons, Cycloryx has been treated as a synonym of Pincerna (see Páll-Gergely 2017). Alycaeus mouhoti has a smoother and larger shell with the simple (not double) peristome than otherwise very similar A. vanbuensis and is also similar to Alycaeus eydouxi (type species of Alycaeus) possessing commonly large and similarly shaped shell with a rather long tube. Alycaeus mouhoti has shell characteristics that connect Alycaeus and Pincerna. Thus, a morphological continuum is present from A. eydouxi, A. mouhoti and A. vanbuensis to A. costulosus, which looks like a typical Cycloryx species. Generic subdivision on this basis would inflate the genus Alycaeus enormously, and A. eydouxi was separated from Pincerna and Stomacosmethis in our molecular phylogeny. Therefore, in this revision by a conservative approach, we included only those species in Alycaeus that are similar to the type species in terms of the very large shell, extremely long sutural tube (and R2) and strongly inflated body whorl.

(5) Chamalycaeus species have a depressed shell with reticulated sculpture and a sutural tube and R2 which vary in length. Pincerna species have higher spire, sculpture dominated by radial ribs and sometimes a short tutural tube. Pincerna crenilabris seemingly connect the two genera by its rather globular shell and medium-sized tube.

(6) The genus Stomacosmethis is characterised by colorful triangular shell mostly with flat whorls and a very short tube. Pincerna species from the distributional range of Stomacosmethis differ by having round whorls and a short tube. All Stomacosmethis species that were examined for radular traits possess unique, simple teeth (Fig. 4H, I). However, a similar type of radula has been found in A. balingensis, which could be classified as Pincerna based on the shell shape (round whorls). For this reason, A. balingensis is here moved to Stomacosmethis. This example suggests that Pincerna and Stomacosmethis might not be mutually monophyletic. Further examinations are necessary to verify the generic position of Pincerna species.

(7) One of the most important results of this study is discovery of distinct differences between Alycaeus and Stomacosmethis, which form two groups without taxa that exhibit overlapping traits of morphology.

Figure 5. 

Relationships between alycaeid genera. Solid lines indicate partly unclear generic borders. See explanation in the text.

In this study we list 412 species-group names including eleven replacement names (seven of them proposed in this study) and five nomina nuda (Table 4). Types of 336 species and subspecies (85%) were examined, and of 19 taxa non-type specimens were examined (5%), whilst we relied on the sufficiently detailed original descriptions of the 22 taxa (6%). For 17 taxa (4%) no material was available to be examined in this study.