Taxonomic assessment of genetically-delineated species of radicine snails (Mollusca, Gastropoda, Lymnaeidae)

The article represents an overview of 29 biological species of the radicine snails (genera Ampullaceana Servain, 1882, Bullastra Bergh, 1901, Racesina Vinarski & Bolotov, 2018, Kamtschaticana Kruglov & Starobogatov, 1984, Myxas G.B. Sowerby I, 1822, Orientogalba Kruglov & Starobogatov, 1985; Peregriana Servain, 1882, Radix Montfort, 1810, and Tibetoradix Bolotov, Vinarski & Aksenova, 2018) recovered during our previous molecular taxonomic study (Aksenova et al. 2018a; Scientific Reports, 8: 11199). For each species, the following information is provided: scientific name, a (non-exhaustive) list of synonyms, type locality, type materials, shell and copulative apparatus morphology, distribution, and nomenclatural and taxonomic remarks. The colour images of shell(s) of each species are also given as well as illustrations of the copulatory apparatuses. We revealed a great conchological variation in the radicines, both intraand interspecific, alongside with striking uniformity in the structure of their copulatory apparatuses. The latter was once thought to be a reliable tool for species delineation and identification in this snail group. The total of 29 species characterised here represents, probably, only a subset of the global taxonomic richness of the radicine snails, which approaches 50 species.


Introduction
Historically, systematics of freshwater pulmonate gastropods had relied on two basic sources of data -conchology and anatomy. The combined use of these sources allowed researchers to delineate species and higher taxa and to compile dichotomous keys for identification of snails (see, for example, Meier-Brook 1983;Taylor 2003;Kruglov 2005). Since the late 1990s, the novel methods of molecular phylogenetics and molecular taxonomy have been widely adopted by malacologists and today they represent a standard tool for species delimitation in different families of freshwater pulmonates. Though there is an almost full agreement that the molecular data are more exact and 'objective' than the morphological ones, their extensive use has led to some problems in the practical taxonomy of aquatic Pulmonata. First, many taxa of snails, established on the basis of morphological information, proved non-valid due to the lack of genetic support (see, for example, Aksenova et al. 2017). On the other hand, some 'good' species defined genetically cannot be identified morphologically as the ranges of their conchological and anatomical variation overlap with those of closely-related species (Schniebs et al. 2011(Schniebs et al. , 2013Aksenova et al. 2018a). The cryptic speciation has also been detected within this group (Bargues et al. 2011;Standley et al. 2013). Lastly, the authors of some recent molecular works, focused on species diversi-ty, prefer to deal with impersonal categories such as MO-TUs (Pfenninger et al. 2006) and clades (von Oheimb et al. 2011;Clewing et al. 2016), instead of scientific names (Latin or latinised binomens) that would correspond to previously-described species of snails. In such cases, the proper taxonomic work remains unfinished since it is very difficult to find correspondence between the MOTUs or impersonal 'clades' and biological species, with their unique names. The use of such nameless entities makes it almost impossible to treat them in accordance with the internationally-adopted rules of zoological nomenclature and impedes the practical issues like conservation planning or studies of the snail-trematode interactions.
Recently, we published a paper (Aksenova et al. 2018a) devoted to the taxonomy, phylogeny and biogeography of the Old World radicine snails (subfamily Amphipepleinae Pini, 1877 of the family Lymnaeidae Rafinesque, 1815), based on an analysis of more than 2600 sequences of two mitochondrial (COI and 16S rRNA) and one nuclear (28S rRNA) gene. This analysis allowed us to propose a new taxonomic structure of the genus Radix Montfort, 1810 s. lato and to recover as many as 35 biological species of radicines, based primarily on the molecular data. Since 2018, one more species of this group, Radix dgebuadzei Aksenova, Vinarski, Bolotov & Kondakov, 2019, has been described (Aksenova et al. 2019). A simplified phylogenetic tree of the recent Amphipepleinae recovered during our work is given in Fig. 1.
In that study (Aksenova et al. 2018a), we tried to link every genetically-defined clade of the genus or species rank to a certain taxonomic name. In particular, we managed to find proper names for formal designation of almost all MOTUs or clades delineated by previous workers (Pfenninger et al. 2006;von Oheimb et al. 2011;Clewing et al. 2016). However, in the previous paper, the emphasis was laid on phylogeny and historical biogeography (Aksenova et al. 2018a). Most issues, related to systematics and nomenclature of the radicines, remained unexplained.
The current study aims at taxononic assessment of the genetically-defined species of the radicine snails. We tried to characterise them both morphologically and geographically and to give the readership some cues on how to identify these molluscs on the basis of their morphological characters. Additionally, we present here some The other Lymnaeidae and outgroup taxa are omitted (see Aksenova et al. 2018a for the complete phylogeny, sequence dataset and methodological details). taxonomic and nomenclatorial considerations aimed to substantiate the taxonomic opinions proposed in the previous article (Aksenova et al. 2018a).

Material and methods
Out of 35 biological species of the radicines delineated by us (Aksenova et al. 2018a), we were able to study morphologically 29 taxa. The rest of the species were included in our analyses on the basis of sequences available from GenBank and we had none of our own or museum materials to examine their morphology. Such species as Radix sp., an (allegedly) endemic to Lake Trichonis of Greece (see Aksenova et al. 2018a) and some taxa from the Tibetan Plateau remain nameless and, though we are aware of their species status, the full absence of the material makes it impossible to form the type series and to designate the holotype as is required by the international rules of zoological nomenclature.
The snails for this study were either collected by the authors from various Old World countries (Russia, China, Tajikistan, Myanmar, Mongolia and some others) or examined in the collections of a series of European zoological institutions. The full enumeration of these repositories are given below, in the abbreviations list. In all cases, when it was possible, we tried to examine the type series of the studied species and to compare the holotype and paratypes (or syntypes) with the published descriptions and our own materials. During our work, we managed to reveal and study the type series (or possible syntypes) of 10 valid species. In some cases, high-quality photos of the type specimens were available for us (for exam-ple, those published in Sitnikova et al. 2012). Besides, we were able to examine the type series of many nominal species considered below as synonyms. Additionally, we substantially benefited from the use of some comprehensive taxonomic publications, including high-quality overviews of the regional faunas (Brandt 1974;Brown 1994;Glöer 2002;Glöer and Pešić 2012;Glöer and Bössneck 2013) and from studies of the type series (Sitnikova et al. 2012(Sitnikova et al. , 2014Vinarski 2016a).
The scheme of shell measurements is given in Fig. 2A. The praeputium:penis sheath ratio has been used as the characteristics of the proportions of the copulatory apparatus (see Fig. 2). This ratio (also known as the 'index of the copulatory organ', ICA) has been used for species delimitation in different genera of the Lymnaeidae (Falniowski 1980;Jackiewicz 1998;Kruglov 2005;Vinarski 2011;Standley et al. 2013). In total, 688 shells of 21 species were measured and 241 specimens of snails were dissected. All measurements in this paper are given in millimetres.
The accounts for particular species presented in the systematic part of this paper include the data on their original descriptions, type locality, type series and distribution. Additionally, we attempted to give morphological descriptions of species, with emphasis on those characters that may help in their identification. We avoided providing the full synonymies for each species since, in some cases, (for such widespread and long studied taxa as Radix auricularia or Peregriana peregra) it would generate enormous lists of synonyms. In most cases, we included into synonymy only names with extant type series or such taxa, whose original descriptions are detailed enough to warrant sure judgements on their taxonomic identity.

TL. Europe.
Types. Possibly lost (Vinarski and Kantor 2016). This species is common in Eurasia, sporadically distributed in North Africa, introduced into North America and New Zealand (Hubendick 1951;Charleston and Climo 1979;Burch 1989;Brown 1994;Kruglov 2005;Andreeva et al. 2010). It has many times been characterised in literature, both conchologically and anatomically (Jackiewicz 1998;Glöer 2002;Kruglov 2005). The typical form of this snail has an ear-shaped shell with shortened spire and greatly expanded body whorl (see Fig. 3A). However, R. auricularia exhibits wide variation is shell shape and proportions (Vinarski 2016b). It may form local and ecological races, including dwarf races of geothermal springs, which had been accepted as valid species (Bolotov et al. 2014;Aksenova et al. 2016Aksenova et al. , 2017. The structure of the copulatory apparatus of R. auricularia is quite typical for the genus. The praeputium is oblong, cylindrical and rather thick; its width is virtually equal along its whole length (see Fig. 4A). The penis sheath is much narrower, with a bulbous swelling on its distal end. The lengths of the praepuptium and the penis sheath of R. auricularia are nearly equal, though in some populations, there is a substantial variation in the ICA values (Vinarski 2011).
According to our data (Aksenova et al. 2018a), R. alticola is endemic to the High Asia mountains; found in Tajikistan (from several sites, including the type locality)  and Nepal. In mountain Tajikistan (Pamir), this species inhabits hot springs and satellite streams with relatively warm water.
The shell shape of R. alticola is similar to that of R. auricularia, but the former species is of much smaller size; its shell height does not exceed 16 mm (see Table 1), whereas the shells of R. auricularia may reach 35-40 mm in height. The proportions of the copulatory organ of R. alticola are very similar to R. auricularia (compare Fig. 3A and 3B).  [Subba Rao 1989;Glöer and Bössneck 2013;Aksenova et al. 2018a]. The record of this species from Tajikistan is based on numerous shells from ZISP collection (see Fig. 3E), virtually identical with the syntypes of R. brevicauda. This species has not been registered from the ex-USSR territory (Vinarski and Kantor 2016) and hereby we, for the first time, include it in the malacofauna of the former Soviet Union. However, this record is still not corroborated genetically.

Radix
The shell of R. brevicauda is ear-shaped, with low spire and greatly expanded aperture. Generally, in many ways, it resembles the shell of R. auricularia and Glöer and Bössneck (2013: 153) note that there are no substantial differences between the two species, which are probable  (15) 21 (0) 29 (11) 16 (9) 26 (20) 40 (0) 12 ( synonyms. However, Annandale and Rao (1925) reported the structure of the jaw and radula of R. brevicauda is distinct from that of R. auricularia. The anatomical structure of the discussed species, described and illustrated by Glöer and Bössneck (2013), is typical for the genus Radix. Our molecular analysis recovered R. brevicauda as a species sister to R. auricularia (Aksenova et al. 2018a).
We may indicate some conchological differences between R. auricularia and R. brevicauda. The latter species is of smaller size, the largest syntype shell is 18.1 mm (our data) and Glöer and Bössneck (2013) mention that R. brevicauda may reach 20 mm in height. Next, the columellar depression in shells of R. brevicauda is very prominent, whereas, in R. auricularia, it is typically weakly developed (compare Fig. 2A and 2D, E). Lastly, the spire whorls in R. auricularia are usually flattened, while in R. brevicauda these are visibly convex and rounded.
Nomenclature remark. The name Limnaea brevicauda Sowerby is the oldest available one to designate a lymnaeid species, sister to R. auricularia, restricted in its distribution to the Central Asia mountain regions. The taxonomic identity of R. brevicauda, as well its close affinity to R. auricularia, was confirmed by the inspection of the extant syntypes.
Types. Not traced, but probably in the Zürich Zoological Museum (Vinarski and Kantor 2016).
We recorded R. euphratica genetically from such remote countries as Iraq and Turkey in the west and southwest and Tajikistan in the northwest, also it has been identified from samples collected in the Krasnodar Region of Russia and Georgia (Aksenova et al. 2018a;see Fig. 5C). The records of this species in literature cover also Afghanistan, India, Iran, Pakistan, Azerbaijan, Tajikistan, Uzbekistan and Turkmenistan (Annandale and Rao 1919a, b;Likharev and Starobogatov 1967;Subba Rao 1989;Kruglov and Starobogatov 1993a;Glöer and Pešić 2012). The range of R. euphratica seems to be rather wide, stretching from the Middle East to northern India. The northernmost localities of this snail are known in the Caucasian region, in Georgia and European Russia (Aksenova et al. 2018a).
Conchologically, R. euphratica may be distinguished from the species of Radix described above by its relatively oblong ovate-conical shell, with high spire and weakly-inflated body whorl. The maximum shell height is around 20.0 mm (see Table 1). The columellar depression is weakly developed and, in some specimens, may be not visible. The tangential line of spire is almost straight or weakly concave that allows us to distinguish this species from the three species of Radix discussed above (see Fig. 3). The morphology of the copulatory apparatus is typical for the genus (see Fig. 4).
Nomenclature remark. Several nominal species of radicines, with type localities situated in the Middle East or the east of Central Asia, were described in the late 19 th -first half of the 20 th century. The oldest of them are Limnaeus tener Küster, 1862, Limnaea auricularia var. persica Bourguignat in Issel, 1865 and Limnaea euphratica Mousson, 1874. The types of L. tener are lost, while the holotype of L. auricularia var. persica is extant (Sitnikova et al. 2012). L. tener and L. auricularia var. persica share the same shell shape; these are ear-shaped, with low spire and enlarged aperture (see Fig. 5A, B). Both species were described from Iran and their conchological similarity, as well as the overlap in geographical distribution, may indicate these forms are conspecific (or represent the intraspecific morphs of R. auricularia). Though the type series of R. euphratica is most probably lost, the shells of this species collected in Iraq (NHMUK) look like shells of snails from Tajikistan studied by us both genetically and morphologically (compare Fig. 3F, G and 3I). It allowed us to select the name Limnaea euphratica Mousson, 1874 for designation of this species, since the shell habitus of both L. tener and L. auricularia var. persica is different from that of snails from Iraq.
The absence of shell picture in the original description of L. euphratica (Mousson, 1874) may be compensated by the author's remark that the shell shape of this species "approaches … some species of the eastern India [such as] L. succinea Desh." (Mousson 1874: 40). Hubendick (1951) regarded L. succinea as a synonym of Lymnaea luteola, whose habitus indeed resembles that of L. euphratica, but looks rather different from shells of either L. tener or L. auricularia var. persica. Based on the original descriptions and the study of specimens from available museum collections (ZISP, NHMUK, NMNH and NHMW), we consider the three taxa from the Middle East, described by Annandale and Prashad (1919), as junior synonyms of R. euphratica. These are Limnaea gedrosiana, L. gedrosiana var. rectilabrum and L. iranica (see Fig. 5D-H). These three species are conchologically very similar and their shell traits correspond well to R. euphratica from Iraq (see Fig. 3I). Specimens of Radix rectilabrum sensu Kruglov and Starobogatov 1993a from Tajikistan and Uzbekistan studied by us (Aksenova et al. 2018a) proved to be genetically indistinguishable from snails sampled in Iraq.
The taxonomic identity of Limnaea tenera and conchologically similar species (Limnaea persica, Limnaea cor Annandale et Prashad, 1919) needs a further research by means of an integrative taxonomic analysis of the topotypic specimens.

TL.
China, Tibet, a roadside ditch west of the Lhasa River mouth, Brahmaputra River basin.
This species, endemic to Tibet, is fully described in our previous paper (Aksenova et al. 2018a), therefore, we give here only pictures of its shell and copulatory organ. Types. Probable syntypes are kept in NHMUK (see Taxonomic remark below).

Radix (Radix) plicatula (Benson in Cantor, 1842)
The actual range of R. plicatula is not ascertained yet. In our molecular analysis, we studied samples of this spe-cies from Beijing, southern and western China that may indicate it is distributed throughout the country. The presence of R. plicatula in adjacent states (Laos, Vietnam) is also very probable, although, as far as we can judge, it is absent from India (Subba Rao 1989). The records of R. auricularia swinhoei (Adams) from Thailand (Brandt 1974) may refer to this species, but a special study is needed to check it.
The shell of R. plicatula is rather oblong, with relatively high spire and moderately inflated body whorl (see Fig. 3J-L). The copulative apparatus is typical for this genus (see Fig. 5D). In all individuals dissected in this study, the penis sheath was slightly longer than the praeputium (see Table 1), thus ICA < 1.0.
Taxonomic remark. Radix plicatula is almost indistinguishable from R. euphratica by its shell habitus (compare Fig. 2F and 2L) and the copulatory organ structure, but molecular analyses have revealed that the two species are distinct and their ranges are almost non-overlapping (Aksenova et al. 2018a). We found the shells of this species, collected in the type locality, in NHMUK (accession No. 42.9.30.50.51.487). These possibly once belonged to Benson's collection and may be considered the probable syntypes (see Fig. 3F). Their morphology is very similar to that in R. plicatula snails examined genetically by us. Having studied the type series of some nominal species of Radix described from China and South-East Asia (kept in NHMUK, NMNH and ZMB), we ascertained they are junior synonyms of R. plicatula (see Vinarski 2016a and synonymy above). TL. The East-Indies. "The original specimens are said to come from Bogor in Java" (Brandt 1974: 230).
This species is endemic to Southeast Asia. Its findings supported by molecular evidence are known from a vast territory, i.e. Thailand, Singapore, Indonesia up to Lesser Sundas (Flores) and Mascarenes (Réunion) [Aksenova et al. 2018a]. Is has also been recorded from Cambodia, Laos and Vietnam (Brandt 1974). However, the identification of R. rubiginosa, based on shell only, may be misleading. As Brandt (1974: 230) stated, "this race has often been confused with L. luteola Lamarck". Therefore, the actual range of R. rubiginosa is not satisfactorily outlined since many historical recordings of it were shell-based.
A high conical spire, almost straight tangential line and weakly-inflated body whorl are the most characteristic conchological traits of R. rubiginosa (see Fig. 6A-C) helping one to distinguish it from the rest of congeners inhabiting the south of Asia. The variation in the proportions of the copulatory organ of this species has not been studied. We dissected four specimens collected from different parts of the R. rubiginosa range (Thailand, Malaysia, Philippines). In all cases, the penis sheath was shorter than the praeputium (see Fig. 4F) and the ICA values varied between 1.02 and 1.59.
Taxonomic remark. R. rubiginosa has an extensive synonymy and a special study is required to clarify the taxonomic identity of numerous nominal species of Radix, described from Indonesia and adjacent countries. Some of these names, such as Radix quadrasi (Möllendorff, 1898) of Philippines, have been used in recent literature, but may well be synonyms of R. rubiginosa (see, for example, Stelbrink et al. 2019).
Remark. Bourguignat (1883: 88), in his lengthy article devoted to classification of continental molluscs of Abyssinia, established two new groups of species within the genus Limnaea -Exsertiana and Raffrayana. He did not give any diagnoses for the two taxa, only lists of species included there. In both cases, these species are currently recognised as junior synonyms of R. natalensis (fide Hubendick 1951;Brown 1994). We selected Exsertiana as a name for designation of a lymnaeid clade containing R. natalensis. Since Bourguignat (1883) did not indicate the type species for Exsertiana, we designate here Limnaeus natalensis var. exsertus Martens, 1866 as the type taxon for this subgenus. This species is usually regarded as identical to R. natalensis (Hubendick, 1951), though Mandahl-Barth (1954) accepted it as a valid species, closely related to the latter.

TL. South Africa, Natal.
Types. Probably lost. We failed to find them either in ZMB collection or in other institutions (NMNH, NHMUK) known to contain vast collections of African aquatic snails.
R. natalensis is widely distributed in the sub-Saharan Africa as well as in the Nile Basin of Northern Africa (van Damme 1984;Brown 1994;Lotfy and Lotfy 2015). It also occurs in Arabia (Neubert 1998) and Atlantic and Indian Ocean islands: Anjouan (Comores), Madagascar (Brown 1994;Stothard et al. 2000) and the Cabo Verde Islands (Aksenova et al. 2018a).
The shell of this species is (in its typical form) ovate-conical, with somewhat oblong and narrow spire and ovoid body whorl (see Fig. 6D, E). However, some varieties of R. natalensis possess an almost spheroid shell with very low spire (see Fig. 6F). The shell height is up to 23 mm (Lotfy and Lotfy 2015).
We studied anatomically a sample of R. natalensis collected from the crater lake Kyamwiga in Uganda and found that the soft body anatomy of this snail is generally the same as in the species of Radix discussed above. Praeputium is relatively narrow and oblong, darkly pigmented (grey), whereas the penis sheath is typically light coloured and much narrower and a little longer than the praeputium (see Fig. 4H); the ratio of their lengths is 0.96 ± 0.07 (see Table 1).
The intraspecific shell variation in R. natalensis is very prominent (see Fig. 6) that led some authors to split this species into several ones (Germain 1919;Mandahl-Barth 1954). Another outcome of this enormous variation is a plethora of nominal species and variety of names proposed to designate the African Radix snails. The synonymy given above represents a small part of this abundance of names (see Germain 1919 for a fuller list of these).  TL. "The East Indies".

Radix
Types. Probably lost. The range of this species covers the central part of the tropical Asia; it is known from India, Nepal and Myanmar, but absent from Thailand (Brandt 1974;Subba Rao 1989;Glöer and Bössneck 2013;Aksenova et al, 2018a).
The shell of R. rufescens is large, its height may approach 45 mm (see Table 1). Most probably, it is the largest member of the genus. Hubendick (1951: 56) described its shape in such words: "[shell is] extremely high and slender. Even the body whorl and the aperture are slender". However, this description is fully applicable only to the typical morph of this species. There are varieties with inflated body whorl and not slender aperture (see Fig. 6I). This high variability allowed some authors to split several intraspecific morphs or even separate species within the R. rufescens s. lato (Troschel 1837; Annandale and Prashad 1919c;Subba Rao 1989).
Some shells of R. rufescens look almost indistinguishable from shells of certain varieties of R. natalensis (compare Fig. 5E and 5H). It is problematic to draw a sharp boundary between the two species on the basis of their conchological characters. R. natalensis and R. rubiginosa represent a pair of closely-related vicariant species isolated by the Middle East, where no representatives of Exsertiana occur. Similar to R. natalensis, the relative height of the spire is the most variable shell trait in R. rufescens.
The next three genera discussed (Ampullaceana, Peregriana and Kamtschaticana) represent the parts of the former subgenus Peregriana s. lato classified within the genus Lymnaea (Kruglov and Starobogatov 1993b;Kruglov 2005) or the genus Radix (Vinarski 2013;Vinarski and Kantor 2016). From the morphological point of view, these three genera cannot be distinguished on the basis of either shell or anatomical characters (Aksenova et al. 2018a) and they share the same Bauplan of the reproductive system. That is why previous authors considered them as the members of a single subgenus (Peregriana; see Kruglov and Starobogatov 1993b;Kruglov 2005) or even lumped them into a single polymorphic species, Lymnaea peregra s. lato (see Hubendick 1951).  Kruglov and Starobogatov (1993b), L. ampullaceus is a valid species allied to A. balthica.
A. ampla is distributed in Europe (except the northernmost and southernmost latitudes), Western Siberia and the southern part of Eastern Siberia (Glöer 2002(Glöer , 2019Vinarski and Glöer 2007;Andreeva et al. 2011;Welter-Schultes 2012). The shell of this species is relatively large, with low spire and very expanded aperture; conchologically, A. ampla can sometimes be confused with R. auricularia; however, the former species has straight or virtually absent columellar fold, which is not characteristic for R. auricularia. Shell height may reach 30-32 mm. The lengths of the praeputium and the penis sheath in this species are roughly equal (see Fig. 8A), with ICA close to 1.00. In a sample of A. ampla (n = 52), collected from several water-bodies of Russia, ICA was equal to 0.88 ± 0.13 (min -max = 0.51-1.21).

Lymnaea dipkunensis
Conchologically, A. dipkunensis resembles A. ampla, but differs from the latter by a slightly higher spire and less inflated aperture. Besides, Kruglov (2005) reported some differences in the proportions of the copulatory organs of these two snails. As was stated above, the penis sheath in A. ampla is slightly longer than the praeputium, whereas, in A. dipkunensis, one may observe an opposite state. According to Kruglov (2005), the praeputium of R. tumida is around 1.7 times longer than the penis sheath. In a sample containing 103 specimens of this species, collected from four localities in Russia, the mean ICA value was 1.84 ± 0.22 (limits of variation: 1.37-2.44) [Vinarski, unpublished data].
Taxonomic remark. Aksenova et al. (2018a) genetically studied some specimens of radicine snails identified  (0) 28 (25) 32 (30) 33 (17) 15 (12) 30 (0) 13 (0) 14 (12) 16 (11) 11 (   as Lymnaea (Peregriana) tumida Held, 1836 sensu Kruglov andStarobogatov (1983b, 1993b) and showed that it is a valid species, distinct from A. ampla. However, to use this species name is hardly acceptable. This taxon is usually considered as an intraspecific morph of Radix auricularia living in large Alpine lakes (Geyer 1927;Glöer 2002). Examination of the topotypes (dried shells) of L. tumida, kept in different European museums (NHMW, NMG, ZMUC), allowed Aksenova et al. (2018a) to agree with this opinion. Therefore, the authors used the next oldest available name, Lymnaea dipkunensis Gundrizer et Starobogatov, 1979, to designate this clade. The identity of this taxon was revealed by means of the inspection of the type series (see also Sitnikova et al. 2014). The records of Lymnaea tumida sensu Kruglov and Starobogatov in the Lower Yenissei Basin (Gundrizer 1984), the type region of L. dipkunensis, give indirect evidence in favour of their identity. However, this taxonomic hypothesis is in need of future integrative research using the topotypes of L. dipkunensis.
Shell ovate-conical, with prominent, but relatively-low spire and moderately-inflated body whorl. Praeputium and penis sheath light-coloured, their lengths are almost equal, though the praeputium is typically slightly longer (see Fig. 8D). The mean values of ICA slightly exceed 1.0 (Kruglov 2005; see also Table 2). According to genetic data, A. fontinalis is distributed in Europe, from Switzerland eastward to south of the European Russia, as well as in Turkey (Aksenova et al. 2018a). The previous recordings of this species from the Urals and Siberia (Kruglov and Starobogatov 1993b;Khokhutkin et al. 2009;Andreeva et al. 2010) require molecular confirmation.

TL. France, Quercy Plateau.
Types. Most probably lost (Mermod 1952). Aksenova et al. (2018a) used the binomen Lymnaea intermedia Lamarck, 1822 to designate a radicine species, sister to A. balthica, which is widely distributed in France and Spain. Since the type specimen, mentioned by Lamarck (1822), is probably lost, we based our understanding of this taxon on examination of both historical samples of it (see, for example, specimen of L. intermedia collected in Lyon, France, in the first half of the 19 th century: Fig. 7I) and some old literary sources, dealing with lymnaeids of Western Europe (Michaud 1831; Küster 1862; Sowerby 1872; Kobelt 1912).
Conchologically, shells of A. intermedia resemble those of A. balthica, but can be distinguished from the latter by higher spire and less inflated body whorl. Modern European authors do not accept A. intermedia as a valid species (Glöer 2002;Welter-Schultes 2012), whereas malacologists of the former USSR still mention this taxon as a species closely allied to A. balthica (Kruglov and Starobogatov 1993b;Khokhutkin et al. 2009;Andreeva et al. 2010;Vinarski and Kantor 2016). The concept of this species proposed by Kruglov andStarobogatov (1983b, 1993b) coincides with that of old European authors (Michaud 1831; Küster 1862; Sowerby 1872). However, we still do not possess any sequence of A. intermedia from the countries lying east of France and the actual range of this species remains unknown. The Russian authors repeatedly recorded this species from different regions of Russia, including the Urals and Siberia (Kruglov and Starobogatov 1993b;Khokhutkin et al. 2009;Andreeva et al. 2010), but all these records were based solely on morphological data and need to be confirmed molecularly.
Lymnaea peregra -Hubendick 1951: 146, figs 1, 9 (partim). Types. Lost (Vinarski and Kantor 2016). This species is characterised conchologically by a relatively oblong shell, with high and narrow spire and moderately-inflated body whorl (see Fig. 7J, K). The structure of the copulatory apparatus in A. lagotis is typical for the genus. Praeputium is relatively long, its length is about 1.5 times larger than the length of the penis sheath (see Fig. 8E; Table 2). The range of A. lagotis covers, almost entirely, Europe, Siberia and some parts of Central Asia, including Tajikistan and western China (Glöer 2002(Glöer , 2019Andreeva et al. 2010;Welter-Schultes 2012;Vinarski and Kantor 2016). The molecularly-confirmed records of this species were reported from different countries of northern, central and southern Europe, as well as from Tajikistan and Siberia (Schniebs et al. 2015;Aksenova et al. 2018a).
Shell proportions of A. lagotis resemble those of A. intermedia; however, A. lagotis typically has a much narrower spire than the latter species (compare Fig. 7I and 7J, K). (Poliński, 1929) Note. This species is endemic to the large ancient lakes of the Balkans (Albrecht et al. 2008;Welter-Schultes 2012;Glöer 2019). A. relicta is phylogenetically close to A. ampla and, most probably, represents a local derivative of the latter originating as a consequence of its ancient invasion into large lakes. As Aksenova et al. (2018a) have shown, this species is polytypic and includes two subspecies, which are separately discussed below.
Types. Whereabouts unknown. This subspecies has been characterised both morphologically and genetically by Albrecht et al. (2008). We examined the copulatory apparatus of two specimens and found that its structure is typical for the genus. Both praeputium and penis sheath are light-coloured; praeuputium is substantially larger than the penis sheath (see Fig. 8M), the ratios between their lengths are 1.42 and 1.46, respectively.
A. r. relicta inhabits Ohrid Lake (Albania and Macedonia), as well the Drin system, at least upstream to the dam Globočičko, approximately 15 km N of the lake (Albrecht et al. 2008).

TL. North Macedonia, Lake Prespa near village of Perovo.
Types. Holotype -SMF; paratypes were placed in NHMW and in a series of private collections in Germany and Hungary (Schütt 1974); currently, specimens from these private collections are kept in the Hungarian Natural History Museum (Budapest) and in the Natural History Museum of Bern (Switzerland). We examined the paratypes kept in NHMW and in the Budapest museum (see Fig. 9B).
This subspecies has been characterised both morphologically and genetically in a series of papers (Schütt 1974;Albrecht et al. 2008;Welter-Schultes 2012). Most authors regard this taxon as a separate species. For example, Albrecht et al. (2008) considered A. r. relicta and A. r. pinteri as two sister species from two 'sister' lakes, Ohrid and Prespa (but see Aksenova et al. 2018a). According to the anatomical data presented in Albrecht et al. (2008), the morphology of the copulatory apparatus in A. r. pinteri is virtually identical with that of the nominative subspecies.
For morphological and molecular characterisation of this species, see Schniebs et al. (2013) and . P. peregra inhabits Europe (except of the northern part), the Urals and the southwest part of Western Siberia (Glöer 2002(Glöer , 2019Khokhutkin et al. 2009;Andreeva et al. 2010;Schniebs et al. 2013;. In many recent publications, this species has been referred to as Radix labiata (Rossmässler, 1835).

Lymnaea gundrizeri
Type series. ZISP (see Sitnikova et al. 2014).  presented a full morphological and molecular account for this species, as well as the data on its range and a comparison with conchologically similar radicine taxa. P. dolgini is a species sister to P. peregra and, probably, represents its vicariant taxon in Northern Asia (Siberia). The molecularly-confirmed recordings of P. dolgini are also known from the north-eastern part of Europe -the Pechora River basin (Aksenova et al. 2018b).
This taxon was introduced as a 'section' of the subgenus Peregriana (Kruglov and Starobogatov 1984). Aksenova et al. (2018a) elevated it to the genus level.
Lectotype. ZISP (see Kruglov and Starobogatov 1984 for details). Aksenova et al. (2016) presented a detailed description of morphology of this snail, accompanied by a molecular analysis of its phylogenetic and taxonomic affinities.  (16) 38 (0) 30 ( Conchologically and anatomically, K. kamtschatica is very similar to other members of the genera Ampullaceana and Peregriana and it is virtually impossible to propose a differential diagnosis for this genus. K. kamtschatica is widely distributed throughout north-eastern Asia, including Kamchatka and Chukotka peninsulas, Transbaikalia and the Amur River basin (Kruglov and Starobogatov 1993b;Aksenova et al. 2016). Possibly, this snail is endemic to Asiatic Russia, though we cannot exclude that it also inhabits Alaska. In Kamchatka, it forms stable populations in the geothermal sites (e.g. the Valley of Geysers) and may live in warm water up to +39.9 °C .
Shell medium-sized (the largest of the two syntypes is 16.9 mm high), with high spire and moderately-inflated body whorl. The shell proportions of T. hookeri resemble those of A. lagotis. The copulatory apparatus is typical for radicines: broad and relatively compact praeputium and very thin and narrow penis sheath (see Fig. 8I); the ratio of their lengths ranges from 1.25-1.50.
T. hookeri is endemic to China. It occurs in Tibet, known from the upstream section of the Lhasa River and a single additional locality (Brahmaputra River basin), altitude range: 4,540-4,980 m. (Aksenova et al. 2018a).
Taxonomic remark. Kruglov and Starobogatov (1993b) classified this species as belonging to the (sub) genus Orientogalba Kruglov et Starobogatov, 1985 and treated it as a senior synonym of Lymnaea heptapotamica Lazareva, 1967, described from southern Kazakhstan.
The examination of the syntypes of L. hookeri has shown that L. heptapotamica should not be synonymised with the former species and may well represent a separate taxon, not related to the genus Tibetoradix.

TL.
Not stated in the original description. Most probably, the type locality should be quoted as Fridrichsdal, a suburb of Copenhagen, Denmark (see Nekhaev et al. 2015 for details).
The taxonomic position and identity of this morphologically-peculiar species have not raised many doubts and most authors treated it more or less identically (Hubendick 1951;Glöer 2002;Welter-Schultes 2012; but see Kruglov and Starobogatov 1993b). The results of our study well correspond to the commonly-accepted concept of M. glutinosa. Shell of this species is very fragile, semi-pellucid and, in a living animal, it is completely covered by the reflected mantle. Shell shape is almost globose, with greatly expanded aperture and very diminished spire (in some specimens, it is almost invisible).
The structure of the copulatory apparatus of M. glutinosa, as is described by various authors (Hubendick 1951;Kruglov and Starobogatov 1985b;Jackiewicz 1998), is virtually indistinguishable from that of the genera Ampullaceana and Peregriana. However, the length of the spermathecal duct is different (long in Myxas, very short or almost absent in Ampullaceana and Peregriana).
The range of M. glutinosa covers Europe (except of the southern and northern parts), the Urals, Western and Central Siberia (Khokhutkin et al. 2009;Welter-Schultes 2012;Vinarski et al. 2013).

Racesina luteola (Lamarck, 1822)
Lymnaea ( TL. India, Bengalia. Types. Not traced, probably in Muséum d'Histoire Naturelle, Genève, Switzerland. A highly-variable species, with several intraspecific 'morphs' differing from each other by their shell shape and proportions (Annandale and Rao 1925;Subba Rao 1989). The typical morph (see Fig. 9I) has ovate shell with more or less prominent and wide spire and weakly-inflated body whorl. Aperture is moderately expanded. Shell surface is smooth and glossy. We had no fixed specimens of R. luteola for dissection; however, according to Hubendick (1951) and Kruglov (2005), the genital morphology of this species generally corresponds to that of the genus Radix, except for the drastically different internal structure of the prostate. Penis sheath is very narrow as compared to thick and oblong praeputium, ICA > 1.00 (Hubendick 1951).
As compared to R. luteola, this snail is characterised by a higher spire and ovate-conical shape of shell. In all other respects, it is conchologically very similar to the type species of the genus. The copulatory apparatus of R. oxiana specimens from Tajikistan, dissected by us, was virtually identical with that of R. luteola from India studied and illustrated by Hubendick (1951). Penis sheath is very narrow, its length is almost equal to length of praeputium or slightly less (see Fig. 8K).
This species of Racesina is distributed in Central Asia (within the ex-USSR boundaries) and Nepal (Aksenova et al. 2018a). The oldest available name, based on a type locality situated within this area, is Limnaeus impurus var. oxiana Boettger, 1889. Though Kruglov and Starobogatov (1993b) treated this taxon as identical with Lymnaea impura, the type locality of the latter species is in India, where R. oxiana does not occur. L. impura is, most probably, a junior synonym of R. luteola (Hubendick 1951;Brandt 1974).
Limnaea luteola f. siamensis - Annandale and Rao 1925: 185, fig. IV(5, 6). Brandt 1974: 232, pl. 16, fig. 98 (partim). Types. Not traced. Aksenova et al. (2018a) used this name as the oldest one applicable to a species of Racesina which is distributed in Myanmar and Thailand. Though Brandt (1974) considered L. siamensis as a junior synonym of Radix rubiginosa, our data show it is untenable. Despite the substantial genetic distance separating Racesina siamensis and R. luteola, we were not able to find prominent morphological differences between them, either in conchological or in anatomical characters. It allows us to treat R. siamensis as a 'cryptic' taxon. Note, however, that we had only a limited number of specimens from Myanmar and some stable morphological differences between the two species will probably be found in future after a thorough study of their intraspecific variation. There is a strong need for a detailed study of genetic diversity and phylogeography of the Racesina luteola species complex.
Morphological note. In a sample of eleven individuals of R. siamensis from Myanmar, dissected by us, five snails had under-developed copulatory apparatuses or lacked them altogether. No signs of a heavy parasite load were seen, thus the hypothesis of the parasitic castration may be rejected. Such a state (aphally) has been registered in different families of freshwater pulmonates, including Physidae, Planorbidae and Lymnaeidae (see Vinarski and Palatov 2018 and references therein). For the radicines, aphally was reported by Arutyunova (1977).
Aphally in aquatic pulmonates is often viewed as an indirect sign of obligate self-fertilisation (autogamy), which may facilitate their introduction into new habitats and rapid establishment of new populations (Beriozkina and Starobogatov 1991;Jarne et al. 1993). Due to a limited sample size, it is unclear whether our finding indicates that R. siamensis is a species prone to self-fertilisation. However, it is a remarkable fact that the aphally was not found during this research in the rest of the radicine species studied anatomically.

Genus Orientogalba Kruglov & Starobogatov, 1985
Orientogalba Kruglov andStarobogatov 1985a: 28. Viridigalba Kruglov andStarobogatov 1985a: 29. Type species. Lymnaea heptapotamica Lazareva, 1967. Kruglov andStarobogatov (1985a) established their subgenus Lymnaea (Orientogalba) to embrace five nominal lymnaeid species distributed in a vast Pacific Region, stretching from north-eastern Asia to the Guam and Hawaii. Though, conchologically, these snails resemble representatives of the genus Galba, their genital morphology is typical for the radicines (Kruglov 2005). The molecular analysis conducted by Aksenova et al. (2018a) has shown that there are at least three biological species within Orientogalba, which are presumably allopatric: O. viridis (Indonesia and Pacific Islands), O. ollula (Far East and, probably, some regions of Central Asia) and O. cf. bowelli (known from Sichuan, China and, probably, also inhabiting Tibet). The actual range of these species remains unknown since only a limited set of sequences has been available. The true species content of Orientogalba is unknown as well, because some nominal species of this genus, such as Orientogalba heptapotamica (Lazareva) and O. lenaensis (Kruglov et Starobogatov, 1985) have not been studied molecularly. The true taxonomic position of "Austropeplea viridis", recently recorded from Spain as an alien species (Schniebs et al. 2017), must also be clarified.
In our opinion, the genus Orientogalba is not a junior synonym of the genus Austropeplea Cotton, 1942, as was suggested by some authors (Ponder and Waterhouse 1997;Schniebs et al. 2017). Our concept of this species is based on the type series of O. viridis (see Fig. 9L). Shell is almost globose, with relatively wide and short spire and heavily-inflated body whorl. Aksenova et al. (2018a) recorded O. viridis from Indonesia. Numerous recordings of this species from other areas, including China, Mongolia, Thailand, Siberia, Spain and some others (Hubendick 1951;Brandt 1974;Kruglov andStarobogatov 1985a, 1993b;Schniebs et al. 2017;Vinarski et al. 2017), were based chiefly on morphological evidence and, therefore, the actual range of O. viridis sensu Aksenova et al. (2018a) is unclear. Table 3 Limnaea ollula Gould 1859: 40.

TL. China, streams and marshes of Hong Kong Island.
Lectotype. National Museum of Natural History, Smithsonian Institution, Washington, USA (Johnson 1964).
Though the type material of L. ollula Gould is extant, we were unable to study it. Instead, we examined a small series of shells of this species collected in Yokohama, Japan (NHMUK). Shell is ovoid, with shortened spire and strongly-inflated body whorls. Generally, it much resembles the shell of O. viridis and we could not delimit these two taxa by means of conchology. Like most species of radicines discussed above, O. ollula is characterised by the disproportion in sizes between the penis sheath and praeputium, the latter being much larger and broader (see Fig. 8M).
Taxonomic remark. This species, described from eastern China, has usually been considered as a junior synonym of O. viridis (Hubendick 1951;Brandt 1974); however, Kruglov and Starobogatov (1993b) regarded it as a separate taxon. The results of our study allowed us to accept their opinion and use the name O. ollula to label a species of Orientogalba, widely distributed in China (found also in South Korea and Nepal). Perhaps, all recordings of "Lymnaea viridis" from Siberia, Russian Far East and Mongolia (Kruglov andStarobogatov 1985a, 1993b;Vinarski and Kantor 2016;Vinarski et al. 2017) should also be referred to as O. ollula.
This poorly-studied species inhabits China: Tibet, Sichuan Province (Subba Rao 1989;Aksenova et al. 2018a) and possibly lives in other parts of the High Asia (Kruglov and Starobogatov 1985a;Kruglov 2005). Conchologically, it represents a typical Orientogalba and the traits allowing one to distinguish it surely from the two above-mentioned species of this genus are unknown. A special study of intraspecific variation in O. cf. bowelli and allied species is needed to delineate them on the basis of morphological data. The data on anatomy of O. cf. bowelli are scarce. Though Kruglov (2005) gave a rather detailed description of its genital morphology, the picture provided by this author (Kruglov 2005: fig. 90) illustrates an animal belonging to the genus Galba, not Orientogalba.
Taxonomic remark. The application of the binomen Limnaea bowelli Preston is difficult. Recent authors tend to consider it as a member of the (sub)genus Galba, whose distribution is restricted to High Asia (Subba Rao 1989;Kruglov 2005;Vinarski and Kantor 2016). On the other hand, Hubendick (1951) hypothesised that Limnaea bowelli is identical with Radix auricularia, whereas Brandt (1974) synonymised L. bowelli with L. viridis. The type series was unavailable for Aksenova et al. (2018a) and the authors conditionally attached the Preston's taxon name to a species of Orientogalba found in Sichuan Province of China. Having examined several small samples of this species kept in NHMUK and NHMN, we found that these shells may belong to Orientogalba; some of them are very similar to shells of O. viridis, whereas others were more or less like Preston's original drawing (see Fig. 9N, O).

Type species. Bullastra velutinoides
Probable syntypes. ZMB (see Vinarski 2016a for details). Hubendick (1951) provided a description of shell, radula and genital morphology of this peculiar species. By its almost globose shell, with extremely reduced spire and extended and reflected mantle border, B. cumingiana superficially resembles M. glutinosa; however, the alleged phylogenetic affinity between the two snails has been rejected by Hubendick (1951) and Kruglov (2005).
Two specimens of B. cumingiana originated from Lake Sampaloc (Philippines, Luzon Island; LMBI collection) were dissected during this study. The structure of the copulatory apparatus is typical for radicines. Praeputium is enlarged and widened, its length is around twice that of the penis sheath length (see Fig. 8N). Penis sheath is short and narrow. The ICA values of the two dissected individuals were 2.11 and 2.13. Both parts of the copulatory apparatus are light-coloured.

Discussion
In this article, we attempted to present the taxonomic accounts for all species of the Old World radicines genetically delineated up to now. The 35 biological species of radicine snails recovered during our molecular taxonomic study (Aksenova et al. 2018a) by no means exhaust the overall diversity of extant species in this group. There are morphologically-distinct species of the radicines still not studied genetically and their actual taxonomic status and phylogenetic affinities remain unclear. Such species of Central Asia as Radix obliquata (Martens, 1864) and R. cucunorica (Möllendorff, 1902) may be mentioned here as two examples. In our opinion, the actual glob-al taxonomic richness of the radicines may approach 50 valid species.
These molluscs exhibit an impressive variation in their shell characters, including shell size, shape, number of whorls, aperture proportions and so on (see Figs 2, 4). Strikingly, this wide repertoire of shell forms is not accompanied by any substantial anatomical diversity. As we tried to show, the structure of the copulatory apparatus remains virtually the same within the Old World radicines (see Figs 3, 7). Although the species slightly differ from each other by the ICA values, the overall morphological scheme of this organ is identical within the group. Though Kruglov (2005) used the ICA as a tool for delineation and identification of radicine species, the usefulness of this ratio for lymnaeid systematics is sometimes questioned. Some authors considered its intraspecific variation too high to provide significant and reproducible results (Schniebs et al. 2011(Schniebs et al. , 2013. Our results have shown that there are no hiatuses in the ICA values of sister species (see Tables 1-3) and, thus, this ratio is almost useless for species diagnostics. Though the species may differ by some qualitative characters, such as pigmentation of praeputium (compare colouration of this organ in two sister species, A. fontinalis and A. lagotis: Fig. 8D, E), we do not have information how widely this trait varies amongst populations of the same species.
A comparison of conchological, anatomical and karyological traits of the radicine genera discussed in Aksenova et al. (2018a) and this paper is given in Table 4. The structure of the copulatory organ within radicines is so uniform that it led some researchers to a drastic reduction of the number of valid species they agreed to accept (see, for example, Hubendick 1951;Jackiewicz 1998). On the other hand, there were malacologists with a strong inclination to species splitting. For example, Kruglov and Starobogatov (1993a, b) delineated more than 90 nominal radicine species within the Northern Eurasia alone. The recent works, based on the integrative taxonomic approach, have shown that many of these nominal taxa lack molecular support and should be synonymised . The ratio between valid and non-valid species in this group may be around 1:4 ). Unfortunately, due to overlap of morphological traits, including both shell and soft body characters, between closely allied species of radicines (Schniebs et al. 2011(Schniebs et al. , 2013, to develop a dichotomous key for identification of snails is next to impossible. The molecular methods are most reliable for species determination in this group (Schniebs et al. 2011(Schniebs et al. , 2013, though there are morphologically-distinct taxa (such as Myxas glutinosa), whose correct identification is possible on the basis of shell characters alone. The use of the reproductive anatomy characters, such as the ICA, is very limited due to the relative uniformity of the copulatory organ structure within the radicines.
Though the evolutionary processes in this group have rarely been studied and discussed, the high species richness and endemism of Radicinae in the mountain part of Central Asia is remarkable. This region forms an obvious hotspot of diversity of this group, with at least one endemic genus (Tibetoradix), which includes not less than six narrow-range species. In addition, at least four species of the genus Radix (R. alticola, R. brevicauda, R. makhrovi, Radix dgebuadzei) are restricted in their distribution to High Asia. This highlights the significance of the region for evolution of the current diversity of the subfamily Amphipepleinae and the probable role of mountain refugia for speciation in lymnaeid snails (see Aksenova et al. 2018a for details).