Sinorachis Wu & Chen

Wu, Min, Chen, Zheyu & Zhang, Liwan, 2019, Jawless land snail Sinorachis, a new bradybaenine genus from China (Eupulmonata, Camaenidae), ZooKeys 893, pp. 51-67 : 51

Sinorachis Wu & Chen gen. nov.

Type species.

Sinorachis baihu Wu & Chen, gen. and sp. nov.

Diagnosis.

Shell conical. Embryonic shell with pits and/or granules. Adult shell smooth. Peristome not reflexed. Head wart developed. Mantle lobe only present on left side. Jaw absent. Membranous sac surrounding terminal genitalia absent. Penis sheath present. Penial caecum absent. Flagellum absent. Dart sac apparatus symmetrical. Mucous glands one; branched.

Description.

Shell conical. Whorls slightly convex. Suture impressed. Protoconch brownish purple; shiny; with tiny pits and/or granules. Adult shell smooth, not hairy or scaly. Body whorl large. Peristome not reflexed. Aperture not expanded. Umbilicus a slit. Shell glossy; banded or not.

General anatomy. Eversible head wart between ommatophore insertions developed. Lobe on mantle collar present on left but absent on right. Jaw absent. Crop thin, indistinguishable from the remaining alimentary tract.

Pallial complex. Ureter closed. Kidney triangular, not bilobed.

Genitalia. Penis sheath present. Penis externally simple; internally with several pilasters. Flagellum absent. Epiphallus and vas deferens distinctly demarcated. Membranous sac surrounding terminal genitalia absent. Dart sac apparatus symmetrical. Accessory sac present. Poly-layered structure developed in dart sac. Mucous gland branched; inserting into dart sac through one peduncle.

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 ).

Remarks.

Sinorachis baihu 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.

The new genus is the only one that lacks a jaw in the subfamily Bradybaeninae. Like Bradybaena Beck, 1837 and some other bradybaenine genera ( Wu et al. 2019), 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.

Figures

Figure 1. Distribution map of Sinorachis Wu & Chen, gen. nov. Blue dot, Sinorachis aureus (Heude, 1890) comb. nov.; yellow dots, Sinorachis onychinus (Heude, 1885) comb. nov.; red dot, Sinorachis baihu Wu & Chen, gen. and sp. nov.

Figure 9. A habitat of Sinorachis baihu Wu & Chen, gen. and sp. nov., HBUMM 08296 - specimen 2, paratype B a diagram showing design of landmarks (solid orange dots) and semi-landmarks (empty orange dots). Arrow indicates the crossing point made by the right profile and the last part of the suture.

Figure 10. Scatter plot of canonical variate 1 against canonical variate 2 (Canonical Variate Analysis), showing the shell morphological relationship among Rachis Albers, 1850 (bright blue dots), Rhachistia Connolly, 1925 (grey-blue dots), Chinese Pseudobuliminus spp. (orange dots), Chinese enid species (grey dots) and Sinorachis gen. nov. (pink dots). a, Sinorachis onychinus (Heude), SMF 42826; b, S. onychinus, SMF 104593; c, S. baihu Wu & Chen, gen. and sp. nov., holotype; d, S. onychinus, SMF 42825; e, S. aureus (Heude), based on an image from Heude (1890); f, S. onychinus, SMF 42827.