Pseudocuneopsis wuana Liu & Wu, 2023

Liu, Lili, Zhang, Liping, Jin, Dandong, Wang, Haotian, Liu, Xiongjun & Wu, Ruiwen, 2023, Molecular and morphological evidence reveals a hidden new taxon in the endemic genus Pseudocuneopsis (Bivalvia, Unionidae) from China, ZooKeys 1179, pp. 219-229 : 219

Pseudocuneopsis wuana Liu & Wu sp. nov.

Fig. 1

Type specimens.

Holotype: China • Guangxi Province, Nanning City (南宁市), Qingshui River (23.4075°N, 108.7557°E), 22 June 2023, Ruiwen Wu leg. (SXNU23062201). Paratypes: same data as holotype (voucher numbers SXNU23062202-SXNU23062206).

Diagnosis.

Pseudocuneopsis wuana sp. nov. is morphologically distinct from the other three recognized species within the genus by shell shape, beak position and sculpture, and surface sculpture (Table 2 ). Diagnostic characteristics: shell ovaliform; ventral margin somewhat prominent at middle; umbo situated 1/3-1/4 of shell length and higher than dorsal margin; epidermis tawny to dark brown, shell surface sculptured with concentric ridges; nacre silvery-white, umbo pocket light yellow.

Description.

Shell ovaliform, medium-thick; anterior margin rounded and inflated; ventral margin somewhat prominent in the middle; umbo located at 1/3-1/4 of shell length and higher than dorsal margin; umbo sculptured with nodes or nodulose wrinkles, or severely eroded; posterior slope formed by ventral margin and dorsal margin low, blunt, located at almost 1/3 of shell height; epidermis tawny to dark brown covered with concentric ridges; anterior adductor muscle scars elliptical, deep, and smooth; posterior adductor muscle scars round to elliptical, shallow and smooth; anterior and posterior retractor muscle scars noticeable, with anterior and posterior irregularly oval; mantle muscle scars obvious; left valve with two separate pseudocardinal teeth and two lateral teeth; outer and inner pseudocardinal teeth of different lengths and projecting outward at different levels, outer and inner pseudocardinal teeth roughly the same size; right valve with one well-developed pseudocardinal tooth and one lateral tooth; nacre silvery-white, umbo pocket light yellow.

Length 24.97-35.91 mm, height 15.49-21.95 mm.

Etymology.

This species’ name is dedicated to Dr Ruiwen Wu, who collected these specimens. For the common name, we recommend "Wu ovaliform Mussel" (English) and "Wu Shi Wei Xie Bang" (武氏伪楔蚌) (Chinese).

Distribution.

Qingshui River, Guangxi, China (Fig. 2 ).

Anatomical characteristics.

Within the incurrent aperture, there are elongated papillae arranged in three or four rows; these have a slight swelling at their base; papillae of the excurrent aperture well developed, stubby, and arranged in two rows. The inner gills are larger than the outer gills. Labial palps are medium-thick and elongated (Fig. 3 ).

Molecular analyses.

Pairwise COI sequence divergences from Pseudocuneopsis wuana sp. nov., P. yangshuoensis , P. capitata , and P. sichuanensis were calculated in MEGA 7.0 with the uncorrected p -distance model. The intraspecific divergence of the newly discovered species, P. wuana sp. nov., ranged from 0% to 0.5%. The genetic divergence between P. wuana and P. yangshuoensis was 5.1%, while that between P. wuana and the other two species, namely P. sichuanensis and P. capitata , was 8.2% and 10.2%, respectively.

The BI and ML trees based on the mitochondrial COI gene yielded incongruent topologies (Figs 4 , 5 ). However, both phylogenetic trees consistently supported the sister-group relationship between Pseudocuneopsis wuana sp. nov. and P. yangshuoensis (BS = 100%; PP = 1.00, Figs 4 , 5 ). The genus Pseudocuneopsis exhibited monophyly with robust bootstrap support (BS = 98%) and full Bayesian posterior probability (PP = 1.00) (Figs 4 , 5 ).

Remarks.

The placement of the new species in Pseudocuneopsis is supported by both morphological characteristics and phylogenetic analyses. Pseudocuneopsis wuana sp. nov. can readily be distinguished from congeneric species by its distinctive ovaliform shell, tawny to dark-brown epidermis covered with concentric ridges, and somewhat prominent at the middle of ventral margin. We conducted an analysis of interspecific divergence among P. sichuanensis , P. capitata , P. yangshuoensis , and the newly described species P. wuana using the COI gene. The results indicate that the genetic distances between P. wuana and its congeneric species, namely P. yangshuoensis , P. sichuanensis , and P. capitata , were 5.1%, 8.2%, and 10.2%, respectively, which are distinctly higher than intraspecific divergences. We conclude that the genetic analyses support the recognition of P. wuana sp. nov. as a valid new species, which can easily be distinguished by its unique COI barcode sequences.

In recent years, through more extensive investigations and field surveys, several new species of freshwater mussels, such as Postolata guangxiensis and Pseudocuneopsis yangshuoensis , have been discovered in Guangxi Province, China ( Dai et al. 2023; Wu et al. 2023). As a major ecological barrier in southwest China, Guangxi is one of the significant watershed areas of the Pearl river basin. The province is noted for its distinctive karst landscape which harbors a rich diversity of species. However, due to the insufficient attention paid to freshwater mussels in the region, the mussel diversity in China is poorly understood. The lack of data regarding species’ distributions, population trends, threats, and accurate taxonomic information has severely impeded conservation efforts for the unionids in this area. Our findings suggest that there is still much to be discovered regarding the diversity of freshwater mussels in Guangxi Province. Additional extensive exploration may reveal other species that have yet to be documented.

Figures

Figure 1. Photographs of Pseudocuneopsis wuana sp. nov. A holotype (SXNU 23062201) B-F paratypes (SXNU 23062202 - SXNU 23062206). All specimens shown at the same scale. Photographs by Lili Liu and Liping Zhang.

Figure 2. The type locality of Pseudocuneopsis wuana sp. nov. in Qingshui River, Nanning City, China.

Figure 3. Anatomical features of Pseudocuneopsis wuana sp. nov. with right valve removed. Abbreviations: aam, anterior adductor muscle; pam, posterior adductor muscle; exa, excurrent aperture; ia, incurrent aperture; f, foot; ig, inner gill; og, outer gill; lp, labial palps; m, mantle; p ia, papillae in incurrent aperture; p exa, papillae in excurrent aperture.

Figure 4. Phylogenetic tree of freshwater mussels inferred by maximum-likelihood (ML) analysis of the COI barcode fragment. Bootstrap-support (BS) values are shown at the nodes. The new species is indicated in red.

Figure 5. Phylogenetic tree of freshwater mussels inferred from Bayesian-inference (BI) analysis of the COI barcode fragment. Posterior probabilities (PP) are shown at the nodes. The new species is indicated in red.