A new Chinese species of Eostrobilops Pilsbry, 1927 with a checklist of Eostrobilops and Enteroplax Gude, 1897 species (Gastropoda, Pulmonata, Strobilopsidae)

Abstract Eostrobilops humicolus Páll-Gergely & Hunyadi, sp. n. is described from Guangxi Province, China. It is characterized by the combination of a small shell (diameter: 2.3–2.4 mm), strongly ribbed dorsal surface, an infraparietal lamella not reaching the callus, and long basal folds. The new species is found approximately 500 and 800 km from the two nearest species Eostrobilops infrequens (northern Vietnam), and Eostrobilops diodontina (Hunan, China), respectively. A checklist of extant Eostrobilops Pilsbry, 1927 and Enteroplax Gude, 1899 species is provided. Enteroplax yaeyamensis Habe & Chinen, 1974, Enteroplax kanjiokuboi Minato & Tada, 1992 and Enteroplax taiwanica Minato & Tada, 1992 are moved to the genus Eostrobilops because of the lack of an elevated parietal callus and a peripheral thread. A map showing all Eostrobilops records is provided.


Introduction
The family Strobilopsidae is mainly defined on a conchological basis; the shell is trochiform, dome-shaped or discoidal, umbilicate and consists of 4.5-6 slowly increasing whorls. The aperture is oblique, peristome more or less thickened and expanded; the ends of the lips are connected by a parietal callus. The main characteristic feature of the family is the armature consisting of two or three parietal lamellae and several deeplyplaced basal folds, all growing continuously from an early neanic state (Pilsbry 1927). Only four species belonging to two genera have been examined anatomically (Baker in Pilsbry 1935, 1948, Minato 1975, Matsumura and Minato 1998. None of these works revealed anatomical characters that would distinguish the Strobilopsidae from other orthurethran families, such as the Pupillidae and Valloniidae (Manganelli et al. 1989). Strobilopsid DNA sequences were published in two works, but neither of them focussed explicitly on the systematic position of the Strobilopsidae. In the phylogenetic tree of Tongkerd et al. (2004), which focussed on the family Hypselostomatidae, Strobilops labyrinthica (Say, 1817) nested within the valloniid clade. The closest taxon to Strobilops is Zoogenetes harpa (Say, 1824) and two samples of Vallonia costata (O. F. Müller, 1774) formed the sister clade of the Strobilops-Zoogenetes clade. The samples of Pupilla (Pupillidae) and Vertigo (Vertiginidae) were more distantly related to Strobilops than to the members of the Valloniidae. In the phylogenetic tree of Wade et al. (2006), which provided an overview of the phylogenetic relationships between most pulmonate groups, Eostrobilops nipponica (Pilsbry, 1908) clustered with Lauria, Pyramidula and Orcula. In this analysis, Vallonia was only included in the larger, orthurethran clade. These data show that Strobilopsidae is an orthurethran family, but its relationships with other families still require clarification.
Living Strobilopsidae occur in America, from northern Mexico to the northern part of South America, and East Asia, from North Korea and south-eastern Russia to southern Borneo (Pilsbry 1927, Kuroda and Miyanaga 1939, Solem 1968, Miller and Christensen 1980, Schileyko 1984, Vermeulen 1992a. Fossil strobilopsids have been reported from Europe, North and South America as well as China (as reviewed by : Wenz 1923, Pilsbry 1927-1935, Manganelli et al. 1989). The oldest fossils that have properly been assigned to the Strobilopsidae dated to the Middle Eocene of Europe. In the New World, fossils no older than from the Late Pliocene can be ascribed to the family. The assignment of Upper Cretaceous-Lower Tertiary Chinese and South American fossils to the Strobilopsidae is speculative only (Manganelli et al. 1989). Pilsbry (1948) proposed that the family Strobilopsidae had radiated from Asia into Europe and the New World. By contrast, Ferreira and Dos Santos Coelho (1970) believed that South America has been the centre of origin of the family. Solem (1979Solem ( , 1981 and Manganelli et al. (1989), however, stated that the radiation from a European centre was much easier to explain, especially if the Cretaceous fossils, which are not certainly strobilopsids, were ignored. Solem (1979Solem ( , 1981 mentioned the Strobilopsidae as one of the most interesting cases of "moved" families, i.e. recent families that live far away from the main stock of their fossil records.
East Asia is inhabited by two recent strobilopsid genera: Enteroplax Gude, 1899 and Eostrobilops Pilsbry, 1927, which differ from each other in the morphology of the parietal callus, the edge of the body whorl and the parietal lamellae. Herein, we describe a new species of Eostrobilops from the Chinese province of Guangxi and provide a critically revised checklist of Eostrobilops and Enteroplax species.

Material and methods
The nomenclature for the armature follows that of Pilsbry (1927). Scanning electron microscopy was undertaken on uncoated shells under a low vacuum SEM (Miniscope TM-1000, Hitachi High-Technologies, Tokyo). We counted shell whorls (to the nearest quarter of a whorl) following Kerney and Cameron (1979).

Abbreviations
Description. Shell small, light brown (only one shell in type material had original colour); trochiform, rather domed above, almost flat ventrally (umbilical side), periphery rounded, very slightly keeled, suture rather deep; 4.75 (n = 3) slowly expanding whorls, protoconch approximately 1.5 whorls; virtually smooth but with weak microscopic pits arranged in irregular radial lines; teleoconch irregularly ribbed; ribs strong dorsally, very weak ventrally (except for inside the umbilicus); spiral structure entirely lacking; umbilicus narrow; inner margin of the whorls exposed in umbilicus irregularly crenulated; aperture semilunar and oblique; peristome slightly thickened and slightly reflexed; parietal callus weak; parietal and infraparietal lamellae well-developed, although the infraparietal does not extend to the peristome; a low interparietal lamella deeply situated, not visible from aperture; three long basal folds and one short columellar lamella; basal folds visible in one specimen with a fresh, translucent shell only (Figs 1D-E, 2). However, this specimen was broken and the fold length can only be estimated (ca. a minimum of a quarter whorl).
Differential diagnosis. Both E. hirasei and E. nipponica are much larger than the new species, they have a more rounded body whorl, wider umbilicus, and weaker dorsal sculpture. Eostrobilops coreana is larger and flatter than E. humicolus sp. n., has a weaker dorsal sculpture, both of its parietal lamellae extend to the peristome, and has a shorter basal folds. Eostrobilops kanjiokuboi is similar to E. humicolus sp. n. by having a strongly ribbed dorsal surface and long basal folds, but differs in the larger size, wider umbilicus, and the serrated lamellae (not serrated in E. humicolus sp. n.); the infraparietal lamella extends to the callus (not in E. humicolus sp. n.), and has a long palatal fold, which is lacking in the new species. Eostrobilops diodontina is slightly larger (D = 2.88, H = 1.75 mm), has more elevated parietal and infraparietal lamellae, and both lamellae attain the peristome. Moreover, E. diodontina has shorter basal folds. Eostrobilops infrequens has a more elevated spire than E. humicolus sp. n., a stronger callus, a narrower umbilicus and shorter basal folds. The spire of E. triptychus is higher, it has more angulate periphery, thicker peristome and shorter basal folds.

Remarks on Eostrobilops species
Solem (1968) named three differences between the two genera: (1) Enteroplax has a raised parietal callus, lacking in Eostrobilops, (2) Enteroplax has a "peripheral thread", lacking in Eostrobilops and (3) Eostrobilops has superior serrated nodes on the parietal lamellae, missing in Enteroplax. The morphology of the callus and the periphery seem to separate the two genera well, because the raised callus is always associated with the peripheral thread and the weak callus is a characteristic feature of species which lack the peripheral thread. The serrated nodes on the lamellae, however, were not observed in at least three species (Eostrobilops infrequens, E. humicolus sp. n. and E. triptychus) which belong to Eostrobilops based on the other two characters. Therefore, the serrated node is excluded from the diagnosis of Eostrobilops. Future investigations may provide additional information on the utility of this character for the subdivision of Eostrobilops. Eostrobilops yaeyamensis, E. taiwanica and E. kanjiokuboi have been described as Enteroplax species. However, they lack the thickened parietal callus, which is conspicuous in every Enteroplax species. Moreover, although they have a somewhat angular periphery, they lack a distinct "peripheral thread", which is also characteristic for Enteroplax. Therefore, all these three species belong to the genus Eostrobilops, as already proposed by Vermeulen (1992a) for E. yaeyamensis.
No obvious teleoconch spiral lines are visible in the photo of the syntype of Eostrobilops diodontina, as noted in the original description (Heude 1885, Pilsbry 1927. The palatal fold, which is approximately a quarter whorl in length and runs just above the keel in the paratype of E. kanjiokuboi (see Material and methods) was not mentioned in the original description. Vermeulen (1992a) compared E. yaeyamensis with E. triptychus. He mentioned that E. yaeyamensis "occasionally shows an interparietalis" and "may have an interparietalis". This information is probably erroneous, because neither the original description (Habe and Chinen 1974), nor Minato (1982) mentioned an interparietalis lamella. Moreover, Vermeulen (1992a) mentioned that E. yaeyamensis has two basal folds, whereas E. triptychus possesses three. However, the description and figure of Minato (1982) describes three basal folds, and interstitial basal plicae were mentioned in the original description of E. yaeyamensis.