The first proven oxychilid land snail endemic to China (Eupulmonata, Gastrodontoidea)

Abstract A new and the first proven oxychilid species endemic to China is reported from Sichuan Province. Sinoxychilusgen. nov. is established based on this new species and has diagnostic traits of the sculptured protoconch, partial epiphallus wrapped by developed penis sheath, penial retractor muscle inserting on the top of penial caecum, spinelets on penial pilasters, absence of epiphallic papilla and perivaginal gland present on vagina and proximal bursa copulatrix duct. In light of shell morphology and through geometric morphometric analyses, Zonites scrobiculatus scrobiculatus Gredler and Z. scrobiculatus hupeina Gredler are proposed to be included in the new genus. A phylogenetic inference based on ITS2 gene indicates that the new genus is systematically close to Oxychilus Fitzinger, which is known from the Western Palearctic and the Southwestern Arabian Peninsula, regions that are geographically far from the distribution range of the new genus.

Gredler (1881) Yen (1939) grouped H. spelaea, H. sekingeriana, and H. franciscana into Kaliella Blanford, 1863and H. zikaveiensis (in Yen 1939sicaveiensis" was a typographical error) into Microcystina Mörch, 1876;he placed H. sinensis, H. planula, H. planata, and H. rejecta in Macrochlamys and moved H. rathouisii to Euplecta Semper, 1870. None of the above mentioned species was anatomically examined. Over-dependence on shell morphology caused many conflicts in the early classification of Chinese species of Hyalina. Furthermore, none of the above-mentioned species that had once been treated as Hyalina has been studied since Yen (1939), and the existence of true oxychilid species in China has been questioned. However, our recent work on the malacofauna of Sichuan, has found a species which meets the morphological definition of Oxychilidae Hess, 1927 but conchologically differs from above-mentioned Hyalina species. The close relationship of the new genus with the oxychilid Oxychilus is also supported by molecular data.

Materials and methods
Four living animals and three empty shells, all fully mature, were collected by hand from the type locality. The living specimens were relaxed by drowning in water before being transferred to 70% ethanol which was replaced with ethanol of the same concentration after three days. The sizes of shell and genitalia of each specimen were measured with calibrated digital Vernier callipers and from photos, both to the nearest 0.1 mm. The number of whorls was recorded with 0.125 whorl accuracy as described by Kerney and Cameron (1979). Soft parts were measured after the specimens were fixed in 70% ethanol.
Chromatographs and sequences were examined and were initially compiled in Sequencher 4.5. The sequence alignment, the evolution model selection and the Maximum Likelihood inference were performed by MEGA 7.0.26 (Kumar et al. 2016). After the data set of internal transcribed spacer 2 (ITS2) were examined by Gblocks 0.91b (Castresana 2000), 58% of the original 950 positions was retained for the final phylogenetic analyses. The Bayesian inference was conducted using MrBayes 3.1 (Ronquist et al. 2012).
Shell morphological variation study was performed in the tps series software including tpsUtil32 (Rohlf 2004), tpsDig32 (Rohlf 2005), using the geometric morphometric (GM) methods based on the landmarks (LMs) and semi-landmarks on the contour of the shell in aperture view (Schilthuizen et al. 2012). The designs of the landmarks and semi-landmarks are as follows: LM1, the columella insertion; LM2, the right insertion of peristome onto body whorl; LM3, the intersection point of right contour and suture of the last whorl; LM4 and LM8, respective right and left extremities on suture; LM5 and LM7, the right and left extremities on suture above LM4 and LM8, respectively; LM6, apex of shell; LMs 9-26, 18 semi-landmarks on the left contour between LM8 and the intersection point of left contour with peristome, by length; LMs 27-44, 18 semi-landmarks on peristome between LM1 and LM2, by length ( Fig. 7; the number on landmarks transferred from semi-landmarks are not shown). The landmarks and the semi-landmarks were treated indiscriminately. The geometric morphometric analysis employed photos of 32 shells in aperture view, including five type specimens of the new species described in this paper, 10 Indian Ariophanta species randomly selected from Raheem et al. (2014), and 15 oxychiline species randomly selected from Sysoev and Schileyko (2009). Full Procrustes fitting, covariance matrix generating, and subsequent canonical variate analysis (CVA) were conducted using MorphoJ (version 1.05f; Klingenberg 2011).
Directions used in descriptions: proximal = towards the genital atrium; distal = away from the genital atrium.

Diagnosis.
Protoconch with intercrossing radial wrinkles and spiral grooves. Penis sheath developed, more or less wrapping partial epiphallus. Tubercles of broken longitudinal penial pilasters bearing spinelets. Penial retractor muscle inserting on the top of penial caecum. Neither flagellum nor epiphallic papilla present. Perivaginal gland present on vagina and proximal bursa copulatrix duct.
Penis sheath present; wrapping partial epiphallus. Penis moderately long and thick; externally simple. Sarcobelum absent. Penial caecum present, having no external demarcation between it and penis. Penial retractor muscle inserting on top of penial caecum. Flagellum absent. Epiphallus thin. Penial caecum internally with transversal ridges near epiphallic pore. Epiphallic papilla absent. Penis internally with developed pilasters. Penial pilasters broken into connected tubercles that each bearing a very short spinelet. Vagina short, internally simple, and without papilla or verge. Perivaginal gland well developed on the surface of vagina and proximal part of bursa copulatrix duct.
Distribution. China (Sichuan, Hunan, Hubei). Etymology. The generic name is a compound of Greek "sino" (= China) and Oxychilus which is a genus of the family Oxychilidae.
Taxonomic remarks. Morphologically, this group belongs to the family Oxychilidae based on the presence of a tripartite sole, oxygnathous jaw, penis sheath, and perivaginal gland and the absence of a caudal horn and sarcobelum, by which Sinoxychilus gen. nov. can be promptly distinguished from Gastrodontidae and Pristilomatidae, the other two families of Gastrodontoidea (sensu Bouchet et al. 2017). The new genus and Oxychilus have many characteristics in common, such as a developed penial caecum, connection of some part of epiphallus + vas deferens and distal penis sheath by connective tissue, as in the European Oxychilus mortilleti (L. Pfeiffer, 1859) (Manganelli and Giusti 1998: figs 5, 10, 13, 14) and in the Asian Araboxychilus sabaeus (Martens, 1889) (Colville and Riedel 1998: fig. 7). However, Sinoxychilus gen. nov. differs from Oxychilus in having an opaque shell with a delicately sculptured protoconch, and in bearing short spinelets on the penial pilasters. The new genus also shows an unusual shell shape, which differs from shells of Ariophanta Desmoulins, 1829 and some other oxychiline genera (Fig. 7).
Riedeliconcha Schileyko, 2003 andVitrinoxychilus Riedel, 1963 are two oxychilid genera which also have spines on the penis inner wall. The new genus differs from them in possessing well-developed penial caecum, penis sheath, and epiphallus, a long bursa copulatrix, and conchologically, an opaque shells with a sculptured protoconch.
Distribution. The new species is known only from its type locality. Etymology. The species is named for the clear demarcation between the leaden black ommatophores and dorsum and the remaining creamy white body, which is reminescent of the giant panda, Ailuropoda melanoleuca by having the color pattern of clear-cut patches of black and white (Fig. 10).
Ecology. The new species was found living in extremely humid environment at type locality. In the laboratory, below 100% relative humidity, animals became active at the relatively lower temperature of 5 °C (Fig. 10) before they were totally inactive at room temperature (ca. 25 °C).
Taxonomic remarks. This new species can be distinguished from all other Chinese Hyalina species in the measurements of its shells (Table 2) and other features. This species, however, as kindly pointed out by Dr Barna Páll-Gergely, is obviously close to Zonites scrobiculatus Gredler, 1885, which was usually treated    . Sinoxychilus melanoleucus gen. nov. and sp. nov., HBUMM08236 specimen 2, paratype A-C indicating that the median part of epiphallus was dissecting out from the penis sheath C arrow indicates epiphallus insertion. Ep-epiphallus; P-penis; PC-penial caecum; PR-penial retractor muscle; PS-penis sheath; VD-vas deferens.    hupeina Yen 1939: 153, pl. 15, fig. 63;Zilch 1974: 199; Coccoglypta (Coccoglypta) scrobiculata hupeina Zilch 1968: 180], by having a distinctly smaller shell, with fewer whorls, and a particular shell shape which is sharply divergent from that of Z. scrobiculatus (Fig. 7). Sinoxychilus melanoleucus is also geographically distant from the geographic range of Z. scrobiculatus (Fig. 1). Nevertheless, we are inclined to believe that based on shell morphology Z. scrobiculatus should belong to Sinoxychilus, although anatomical and molecular evidence is unavailable.
With the exception of two genera distributed in the southwestern part of the Arabian Peninsula, oxychilid snails are only known from the Western Palearctic (Neubert 1998;Schileyko 2003). The new species described herein, and its congeners, are undoubtedly the easternmost representatives of Oxychilidae, which suggests that Sinoxychilus might be an isolated group in China, remote from the main distribution area of the family.