Jawless land snail Sinorachis, a new bradybaenine genus from China (Eupulmonata, Camaenidae)

Abstract A new land snail species that represents a new genus is reported from Hubei, China. The snail has a conical shell with pits and/or granules on embryonic whorls and a smooth teleoconch with straight peristome. The head of the animal has a developed wart. The mantle lobe is only developed on the left side. At the front of the buccal mass there is no chitinous jaw that is without exception seen in Chinese camaenids. Its radular teeth are usually slender and tongue-shaped, not typical in bradybaenine snails. The genital system is typical of Bradybaeninae and is characterized by the absence of a membranous sac surrounding the terminal genitalia, penial caecum or flagellum; a well-developed penis sheath; a symmetrical dart sac apparatus; and one distally branched mucous gland. The new species Sinorachis baihu Wu & Chen, gen. and sp. nov., is assigned to the type species of the new genus, in which all the known Chinese Rachis species are included. Thereby, the new genus is composed of three species, namely Sinorachis onychinus (Heude), comb. nov., Sinorachis aureus (Heude), comb. nov. and the new species.


Introduction
Rachis Albers, 1850 (type species Bulimus punctatus Anton, 1838; SD Martens in Albers 1860) is an enoid genus comprised of many known species from Africa and India (Schileyko 1998b). Two Chinese land snail species with conical shells were assigned to this genus based on shell morphology (Gredler 1887;Yen 1939;Wu 2018). Although Möllendorff (1901) placed them in Buliminus and thought they appeared to be related to the group, including Bulimus cantori Philippi, 1844 (= Mirus cantori), he wondered about the absence of an angular nodule that is ubiquitously observed in the Chinese enids. The Chinese Rachis species differed from the true Rachis species by the presence of embryonic shell sculpture that is unseen in Rachis (Schileyko 1998b). However, this sculpture may have been overlooked by early researchers.
The shells of Chinese Rachis species are, in many respects, untypical of the bradybaenine genera. In our recent work on the land snails from Hubei Province, comparison of the shell morphology revealed an arboreal snail that was firmly believed to fall into the same category of Chinese Rachis. The genital pattern of this species, however, totally differs from those of these enoids; rather, the developed dart sac apparatus suggests it belongs to the camaenid subfamily Bradybaeninae.

Materials and methods
Living specimens were relaxed by drowning in fresh water before being transferred to 70% ethanol for fixation, which was replaced with ethanol of the same concentration after three days. Just after the specimens were relaxed, a piece of foot was cut and preserved in 99.7% ethanol for future molecular analysis. The shell and genitalia were measured with digital vernier calipers and from photographs to the nearest 0.1 mm. Whorl number was recorded as described by Kerney and Cameron (1979), with 0.125 (= 1 / 8 ) whorl accuracy. Soft parts were measured after the specimens were sufficiently fixed in 70% ethanol. Directions used in descriptions: proximal = towards the genital atrium; distal = away from the genital atrium.
The buccal mass was removed and treated in 10% sodium hydroxide solution under 60 degrees Celsius for up to 10 min before extracting the radula, which was cleaned by water using an ultrasonic cleaner. Then the radula was transferred into 75% ethanol. Radulae and shell were examined under a scanning election microscope (Sigma 500).
Geometric morphometric methods were used to explore the conchological relationship among the new species described herein, the enoids and the high-shelled bradybaenine species distributed in mainland China. Shell morphological variation analyses were performed in the tps series software including tpsUtil32 (Rohlf 2004) and tpsDig32 (Rohlf 2005), using the geometric morphometric methods based on the landmarks and semi-landmarks on the profile of the aperture-viewed shell as per Schilthuizen et al. (2012). The designs of the landmarks and semi-landmarks are as follows (Fig. 9B):

LM1
the crossing of peristome and left profile of body whorl; LM2 the columella insertion; LM3 the right insertion of peristome onto body whorl; LM4 and LM10 the right and left terminal points on last suture, respectively; LM5 and LM9 the right and left terminal points on penultimate suture, respectively; LM6 and LM8 the right and left terminal points on suture above the penultimate one, respectively; LM7 apex of shell; LM11-18 eight semi-landmarks on the left profile between LM10 and LM1 by length; LM19-36 eighteen semi-landmarks on the peristome between LM1 and LM3 by length.
The usually used landmark point crossed by the right profile and the last part of suture (arrowed on Fig. 9B) was not chosen in this study because the point is not present on all the aperture-view images of the specimens observed herein. The landmarks and the semi-landmarks were treated indiscriminately. The geometric morphometric analysis employed aperture-viewed images of a total of 232 shells including most of Chinese enids (112 specimens of 112 species, including one from Wu and Xu 2011, 111 from Wu 2018; see Appendix 1), some Chinese Pseudobuliminus Gredler, 1886 and one Stenogyropsis Möllendorff, 1899 species (102 specimens of 20 species: SMF and HBUMM specimens; see Appendix 1), Rachis Albers, 1850 (five specimens of two species: SMF specimens and Raheem et al. 2014: fig. 39a; see Appendix 1) and Rhachistia Connolly, 1925  Etymology. This new genus is named after sino (China) and rachis, an enoid genus in which the old species of the new genus were placed.
Distribution. Hubei (Badong, Lichuan), Chongqing (Chengkou), Yunnan (Dali) (Fig. 1).  Wu & Chen, gen. and sp. nov. shares most conchological features with the other two known species, namely Buliminus onychinus Heude, 1885 and Buliminus aureus Heude, 1890, which were treated by some authors as species of the enoid genus Rachis (Gredler 1887). But based on pallial complex and genital system, the new species described herein should not been assigned to the genus Rachis Albers, 1850 (Enoidea) that belongs to Orthurethra and there is no dart apparatus in genitalia. The new genus is entirely in character for the subfamily Bradybaeninae in possessing the typical dart sac apparatus that does not differ from that commonly seen in all the Chinese bradybaenine genera. In our opinion, based on shell morphology, B. onychinus and B. aureus should also belong to the genus Sinorachis gen. nov.

Remarks. Sinorachis baihu
The new genus is the only one that lacks a jaw in the subfamily Bradybaeninae. Like Bradybaena Beck, 1837 and some other bradybaenine genera , the genus shows a leaf-shaped appendage on the left mantle collar. The shells of the new genus are quite different from those of the high-shelled genus Pseudobuliminus Gredler, 1886 in having a sculptured embryonic shell and a distinctly large body whorl. In aspects of general shell morphology, the shell of the new genus, the genus Rachis Albers, 1850 distributed in Africa and India, the genus Rhachistia Connolly, 1925 distributed in eastern Africa and Asia, Chinese enid genus and Chinese Pseudobuliminus spp. can be discriminated with the aid of the geometric morphometric methods (Fig. 10) based on the landmarking scheme employed herein (Fig. 9B).
In comparison with Chinese species of another bradybaenine genus, Pseudobuliminus, that also has a high spired adult shell and embryonic sculpture, the new genus has a poly-layered structure, an accessory sac, and a single branch of mucous gland in the dart sac apparatus, but has no membranous sac surrounding terminal genitalia. If only focusing on the characteristic spectrum of genitalia (table 1, in Wu 2019), the genus is closest to Ponsadenia Schileyko, 1978 but these two genera can be distinguished by presence/absence of the poly-layered shell structure and the structure of accessory sac which looks like a bridge in the latter genus. HBUMM08296-specimen 1. Paratype: one juvenile animal; same data as for preceding; HBUMM08296-specimen 2. Partial foot was cut off in both specimens and preserved in 99.7% ethanol at -20 °C; HBUMM08296a-specimens 1, 2.

Description. Shell
General anatomy (Figs 3, 4). A crest-like head wart between and slightly behind ommatophore insertions present. On left edge of mantle collar a leaf-shaped appendage present. Body dorsally white; symmetrically with two lateral black pigmented stripes that become lighter near sole. Sole creamy white. Jaw absent (Fig. 4C, D, G).
Pallial complex (Fig. 5). Pallial roof not pigmented. Pallial gland thin, parallel to mantle collar. Hindgut running parallel to parietal-palatal margin for length of pallial chamber. Ureter slender, typical sigmurethrous, about 1/5 breadth of hindgut, adhering to hindgut for all its length. Secondary ureter developed. Kidney triangular, not bilobed, about as long as 1/2 of pallial chamber. Heart as long as 1/3 -1/2 of kidney. Main pulmonary vein running along contour and apex of kidney, then diffusing into thinner veins mostly concentrated on anterior half. Radula (Fig. 6A-C): Teeth arranged in transversal rows, each row containing about 151 (75-1-75) closely arranged teeth. Central tooth tricuspid, narrowly tongueshaped (Fig. 6A). Lateral teeth slightly thickened at inner edge; bicuspid (L1-2 or A left margin of mantle collar with the lobe arrowed B right margin of mantle collar C lateral dorsal view of buccal mass with an oral curtain (a sheet of curtain-like tissue on the most anterior of the buccal mass) arrowed D dorsal view of buccal mass with an oral curtain arrowed E shell-removed animal, showing three pigmentation patches near mantle margin F internal body wall of head, showing no obvious head gland between the ommatophore tentacles G HBUMM08296-specimen 2, paratype, mouth of ventral view with an oral curtain arrowed. L1-3) (Fig. 6A), tricuspid (from L2 or L3 on) (Fig. 6A, B) and gradually transformed to marginals with one endocone and three or four ectocones (Fig. 6C).
Genital system (Figs 7, 8). Penis sheath long, covering approximately 3/4 of penis. Penis thin; externally simple; internally with three pilasters. Epiphallus subequal to penis in length; without epiphallic papilla. Flagellum absent. Vas deferens ca. 1/2 length of epiphallus; of even thickness. Epiphallus and vas deferens sharply demarcated (Fig. 7). Dart sac apparatus large in size; distal 1/3 with a distinct accessory sac ventrally that is internally solid. Love dart very short, approximate 0.7 mm long; sharply tapering from distal end; transparent. Mucous gland with one common peduncle; simply branched. Vagina as long as penis. Bursa copulatrix small, ball-shaped.
Etymology. This species is named after baihu (=白虎in Chinese, means white tiger) which is the totem of the local Tujia people.

Distribution. Hubei.
Ecology. This species was only found on the trunk of a tree (Fig. 9A). Taxonomic remarks. The new species and the two species that were once placed in the genus Rachis share many conchological features. However, typical sigmurethrous pallial complex (Solem 1985) is observed in the new species. The new species is slightly smaller than and obviously thinner than Sinorachis onychinus (height 16 mm, diam. and is axially wrinkled on the subsequent protoconch whorls (0.5-1.25 whorl). On the remaining embryonic whorls, the sculpture is shown as evenly distributed tiny pits [examined material: SMF42825, SMF42826: Patung, Hupei, Mlldff. G., Slg. Kobelt u. Bttgr. SMF42827: Sinorachis onychinus (not paratypes of Rhachis chalcedonicus as mentioned in Yen 1939: 91, pl. 8, fig. 47), SW Hubei, Gredler G., Slg. Mlldff. SMF1045593] that become weak or disappear altogether.
In pulmonates the presence of a jaw is a ubiquitous characteristic related to herbivorous/ detritivorous/ fungivorous foraging strategies, while the absence of a jaw is correlated with predation/carnivorous foraging strategies (Mordan and Wade 2008). In addition, the absence of a jaw also occurs in some non-carnivorous groups, such as Achatinellidae, which are fungivorous and have the jaw weakly developed or absent (Schileyko 1998a). The comparison between the new species and Laeocathaica prionotropis Möllendorff, 1899 (Bradybaeninae) (Fig. 6F, G. HBUMM08299-spec. 1, Bikou, Wenxian, Gansu. Coll. Li, Q., April 2019) indicates they are two different types of radula. The latter species, a typical ground-dweller, is herbivorous snail, which has the robust cone-shaped and sparsely arranged radular teeth that seem to be typical Figure 8. Sinorachis baihu Wu & Chen, gen. and sp. nov., HBUMM08296-specimen 1, holotype A bottom view of dart sac apparatus B partial dorsally exposed dart sac apparatus, showing arrowed poly-layered structure C distal part of dorsally exposed dart sac apparatus, showing opened love dart chamber, with opening of the love dart chamber arrowed D dorsally exposed dart sac apparatus with opening of love dart chamber arrowed.
in bradybaenine snails (e.g., compare it with fig. 4 in Páll-Gergely and Hunyadi 2016), while the new species has more slender and densely arranged radular teeth, which suggest the diet range of this species might not cover large plants and animals.