﻿New camaenid genus and species from Zhejiang, East China (Eupulmonata, Helicoidea)

﻿Abstract We report a new land snail species representing a new genus from the mountainous area of Zhejiang, China. The snail has a depressed shell with granules all over the surface. The soft part of the new taxon is characterized by the presence of a mantle lobe whose form is reviewed herein across a wide range of helicoid snails, the presence of a developed epiphallic papilla, and the absence of a penial sheath, a dart sac apparatus and a flagellum. As indicated by a molecular-based phylogeny (16S + ITS2), the new taxon is deeply nested in the eastern Asian camaenid genera and shows a close relationship with the camaenids distributed in Central China.

In contrast to the northern parts of East China, more than 74% of the mountainous area in Zhejiang provides a considerable variety of microhabitats where speciation of land snails is expected.We have recently found a camaenid slightly smaller than Nesiohelix moreletiana and N. yeni in shell size that represents an unknown camaenid in terms of genital anatomy and molecular systematics.The presence of a lobe on the mantle collar in this new snail impels us to compare this body part in a wider range of helicoid snails.

Morphology
Living specimens were relaxed by drowning in water and then fixed in 70% ethanol.The shell and genital system were measured with digital vernier calipers and from photograph to the nearest 0.1 mm, respectively.Whorl number was counted as described by Kerney and Cameron (1979), with 0.125 (= 1 / 8 ) whorls accuracy.Parts of the genital system were measured after the specimens were sufficiently fixed in 70% ethanol.Radula preparation: The buccal mass was removed and treated in 10% sodium hydroxide solution below 60 °C for up to 10 min before the radula was extracted.The released radula was cleaned with water using a sonic cleaner and then transferred into 75% ethanol before being mounted.The radula was examined under a scanning electron microscope (SEM; Sigma 500).To observe the possible lobe near the mantle edge, the hardened mucus and small pieces of dirt were carefully removed with a soft brush under water.Directions used in descriptions: proximal = towards the genital atrium; distal = away from the genital atrium.
The Chinese name for the person, new taxon or locality is provided only once in square brackets when necessary.

Phylogeny of the studied taxa
A concatenated matrix of 80 terminals (including outgroup) × 1045 bp (296 bp from partial 16S sequence and 749 bp from partial ITS2 sequence) was used in the subsequent analyses.Both 16S and ITS2 were unsaturated.For the Bayesian method, GTR+F+I+G4 was selected as the best evolution model for 16S, as well as K2P+G4 for ITS2.For the ML method, GTR+F+I+G4 was the best model for 16S I and K2P+I+I+R2 was the best model for ITS2.The obtained phylograms using Bayesian inference and the maximum-likelihood analysis are topologically similar to each other except for two positions, as indicated in Fig. 7. Most clades received high support.The genera Nesiohelix Kuroda & Emura, 1943, Traumatophora Ancey, 1887, Camaenella Pilsbry, 1893, Aegista, Plectotropis Martens, 1860 are basal on the tree.Sinocamaena gen.nov. is inside the clade consisting of a variety of taxa that are almost exclusively endemic to the Southern Gansu Plateau.The phylogram topologically agrees well with that of Wu et al. (2023).

Comparative study of the mantle lobe in helicoids, especially for eastern Asian taxa
In some preserved specimens, the mantle lobe is covered with curdled mucus and is difficult to observe.At the mantle collar, the lobe-like flesh (literally indistinguishable from "lobe", e.g., in Chen et al. 2021) near the anus+ pneumostome, forms a more or less developed elongating part of the structure of the anus orifice, i.e., the suprapneumostomal and subpneumostomal lobes (e.g., in Napaeus nanodes, fig.6A in Henríquez et al. 1993).In this work, the mantle lobe refers to a single separate piece of fleshy lamina (e.g., Fig. 3B) on the opposite side of the lobe-like structure near the anus + pneumostome (e.g., Fig. 3A), which appears as a thin fleshy flap that is usually attached to the inner wall of the mantle collar.If present, the mantle lobe of a dextral-shelled snail is on the left side, and in the case of a sinistral-shelled snail on the right side of the mantle collar.

Systematics
General anatomy.A small pore externally present between ommatophore insertions.Eversible head wart very weakly developed.A mantle lobe present.
Etymology.This new genus is named after "sino" (= China) and "camaena" which is a camaenid genus that includes many large-sized helicoid species.
Remarks.The new genus is conchologically close to many camaenids, such as Camaena Albers, 1850 and Burmochloritis Godwin-Austen, 1920, in having a large helicoid shell with multiple slender bands.In comparison to Camaena (sensu Schileyko 2003), the new genus has a strongly sculptured protoconch and an extremely short epiphallus (the part between penial retractor muscle insertion and vas deferens insertion), but has neither the axial corrugated pilasters within penis nor the flagellum.The new genus differs from Burmochloritis (Páll-Gergely et al. 2023) in the absence of the flagellum, the long cylin-drical epiphallus, the penial caecum and the dart sac.Sinocamaena gen.nov. shares with Sinochloritis the possession of granules on the protoconch and the characters from both general and genital anatomy, including the presence of a visible gland pore between the ommatophore insertions, a mantle lobe, a well-developed epiphallic papilla and the absence of a penial sheath and a dart sac apparatus.Compared to Sinochloritis, the new taxon has neither a flagellum nor a long epiphallus with the cylindrical trunk, nor prominent penial pilasters.In terms of shell morphology, generally, the new genus looks different from any other Chinese indigenous camaenid genus.Regardless of the shell morphology, all the other Chinese camaenid genera having no dart sac apparatus, i.e., Amphidromus Albers, 1850, Landouria Godwin-Austen, 1918, Pancala Kuroda & Habe, 1949, Satsuma, Yakuchloritis Habe, 1955, Pseudostegodera and the above mentioned Sinochloritis, possess a well-developed flagellum in the male part of genitalia (table 1 in Wu 2023).The present phylogeny (Fig. 7) suggests that the new taxon is possibly the nearest relative of almost all the members of dart sac-bearing bradybaenines endemic to the South Gansu Plateau or Central China.
It is noteworthy that the taxa that are basal on the phylogram, i.e., Nesiohelix, Traumatophora, Acusta, Bradybaena, Plectotropis, Aegista, Euhadra, Satsuma, Camaena, have mantle lobes.In general, the camaenids from Central China constitute a monophyly that receives high support values (clade X in Fig. 7), in which all terminals have a dart sac apparatus but lack a mantle lobe.The extended study of mantle lobes in helicoids taken here suggests that the presence of the mantle lobe could be a widely distributed and possibly a plesiomorphic character in the superfamily Helicoidea.
General anatomy (Figs 2-4).Externally, a small pore present between ommatophore insertions.Eversible head wart surrounding the pore very weakly present.A mantle lobe present.Tentacles and body in dark leaden-black; sole in color lighter than dorsal side.Jaw arcuate; with 12 more or less projecting ribs (Fig. 3H).Radula (HBUMM08367-spec. 1) comprises numerous transverse rows of teeth, each row containing approximately 131 teeth, 38+27+1+27+38.Central tooth symmetrically conic, without cuspid.Lateral tooth about more than two times larger than central tooth, strong conic medially, weakly uni-cuspid at both sides.Marginal teeth gradually changing from broadly tri-cuspid to tetra-cuspid (Fig. 4).Genitalia (Figs 5,6).Penial sheath absent.Penis club-shaped, swollen near insertion of penial retractor muscle.Penis externally simple, internally with numerous longitudinal arranged low projections like scales, which do not connect to each other into pilasters along the penial inner wall.Epiphallic papilla rather developed, on side of penial retractor muscle insertion with about several longitudinal pilasters which join apically.Epiphallus very short and stout, internally with a septum longitudinally dividing epiphallus into two separate chambers which one is empty and another one with about 10 pieces of high and low pilas- Remarks.The new species and Camaena vulpis (Gredler, 1887) are superficially similar in having the densely and minutely granulate surface, numerous spiral thin bands and the general shape of shell.However, besides possessing a distinctly larger shell and a higher spire, the latter species has a totally differ- The phylogenetic analysis suggested that the new species/genus and the taxa distributed in Central China are possibly close relatives (Fig. 7).For other comments see the genus.where the BI tree topologically differs from the ML tree.Red dot/green dot indicates every terminal on that branch that has/has not a mantle lobe.An asterisk after the species name indicates that observation of the mantle lobe failed due to the bad condition of the specimen.The species under the genera in quotes are thought to be questionable generic assignments (Wu et al. 2023).

HBUMM
mollusc collection of the Museum of Hebei University, Baoding, China IZCAS Zoological Museum, Institute of Zoology, Chinese Academy of Sciences, Beijing, China

Figure 3 .
Figure 3. Sinocamaena cheni Wu, gen.et sp.nov., general anatomy A-C holotype, HBUMM08381-spec.1 A lobe-like structure near the anus+ pneumostome B mantle lobe on the left margin of mantle collar C anterior part of the animal, dorsal view, between ommatophore tentacles, showing the head gland where the pore/opening is not obvious D-H paratype, HBUMM08367-spec.1 D lobe-like structure near the anus+ pneumostome E mantle lobe on the left margin of mantle collar F dorsal view of anterior part of the animal, showing the pore among the contractive head gland G internal body wall of head, showing the head gland pore between the ommatophore tentacles H jaw, with basal muscle tissue remaining.

Figure 7 .
Figure 7. Maximum-likelihood phylogram based on the concatenated partial mitochondrial 16S and partial ITS2 sequences of East Asian camaenid species.The tree is rooted on Helix pomatia.Numbers near nodes indicate the Shimodaira and Hasegawa-approximate likelihood-ratios (SH-aLRT)/approximate Bayes test (aBayes)/ultra-fast bootstrap (IQ-TREE, maximum likelihood)/posterior probability (MrBayes, Bayesian inference).An asterisk on the branch indicates a clade with all well-supported values (SH-aLRT ≥ 80%, aBayes ≥ 0.95, BS ≥ 95%, PP ≥ 0.95).The broken branch indicates that the branch is shortened to exactly 1/2 the original length.Scale bar is for substitutions per site.Orange branches indicatewhere the BI tree topologically differs from the ML tree.Red dot/green dot indicates every terminal on that branch that has/has not a mantle lobe.An asterisk after the species name indicates that observation of the mantle lobe failed due to the bad condition of the specimen.The species under the genera in quotes are thought to be questionable generic assignments(Wu et al. 2023).

Table 1
Material examined for the comparative morphology of the mantle lobe in some helicoids.