Sinoxychilus, Wu, Min & Liu, Zhengping, 2019

Wu, Min & Liu, Zhengping, 2019, The first proven oxychilid land snail endemic to China (Eupulmonata, Gastrodontoidea), ZooKeys 870, pp. 33-50 : 35-37

Sinoxychilus gen. nov.

Type species.

Sinoxychilus melanoleucus gen. nov. and sp. nov.

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.

Description.

Shell depressed; thin; opaque; of about 4.5 whorls. Umbilicus moderately wide. Protoconch with intercrossing radial wrinkles and spiral grooves. Teleoconch with spiral furrows. Aperture somewhat sinuate at peristome. Aperture toothless, unexpanded.

Sole tripartite. Caudal foss or caudal horn absent. Jaw oxygnathous, with median projection.

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 .

Molecular phylogenetic analyses.

The examined ITS2 sequences are from GenBank and this study. According to Hausdorf (2000), Gastrodontoidea is made up of six families, namely Pristilomatidae Cockerell, 1891, Chronidae Thiele, 1931, Euconulidae H. B. Baker, 1928, Trochomorphidae Möllendorff, 1890, Gastrodontidae Tryon, 1866, and Oxychilidae . After searching for ITS2 sequences from these six families in NCBI (https://www.ncbi.nlm.nih.gov/), 21 ITS2 haplotypes of Euconulus spp. ( Euconulidae ), Oxychilus spp. ( Oxychilidae ), and one Vitrea species ( Pristilomatidae ) were added to our analyses (Table 1). After eliminating poorly aligned positions and divergent regions of the alignment, a dataset of 25 × 552 bp was used for the subsequent analyses. The "T92 (Tamura 3-parameter) + G" model was chosen as the best nucleotide substitution model because of the lowest AIC score (lnL = −1746.871, AICc = 3594.112). The phylograms produced by the Maximum Likelihood Inference and the Bayesian Inference are topologically identical ( Fig. 8 ). The obtained phylogenetic inference shows Sinoxychilus gen. nov. forms a sister group with the genus Oxychilus , and both genera are well embedded in the Gastrodontoidea clade ( Fig. 8 ).

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 ).

Zonites scrobiculatus scrobiculatus Gredler, 1885 and Z. scrobiculatus hupeina Gredler, 1887 are included in the new genus although they are only known conchologically (see Taxonomic remarks below).

Riedeliconcha Schileyko, 2003 and Vitrinoxychilus 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.

Figures

Figure 7. Scatter plot of canonical variate 1 against canonical variate 2 (yielded by canonical variate analysis), showing morphological relationship among Sinoxychilus melanoleucus gen. nov. and sp. nov. (red dots), Zonites scrobiculatus scrobiculatus Gredler, 1885 and Zonites scrobiculatus hupeina Gredler, 1887 (light blue dots), Indian Ariophanta spp. (Raheem et al. 2014) (dark blue dots) and oxychiline spp. (Sysoev and Schileyko 2009) (orange dots). A diagram showing design of landmarks (numbered) and semi-landmarks (not numbered) is provided.

Figure 8. Maximum likelihood tree based on ITS 2 gene (- ln likelihood = − 1746.99). Ingroups: Euconulus Reinhardt, 1883 (Euconulidae), Vitrea Fitzinger, 1833 (Pristilomatidae), Oxychilus Fitzinger, 1833 (Oxychilidae), and Sinoxychilus gen. nov. (Oxychilidae). This ML tree shares the same topology with the Bayesian Inference tree. Numbers on branches indicate maximum likelihood and Bayesian posterior probabilities.