Inversidens rentianensis Wu & Wu, 2021

Wu, Ruiwen, Liu, Xiongjun, Kondo, Takaki, Ouyang, Shan & Wu, Xiaoping, 2021, New species of the genus Inversidens Haas, 1911 (Unionoida, Unionidae, Gonideinae) from Jiangxi Province, China, ZooKeys 1054, pp. 85-93 : 85

Inversidens rentianensis Wu & Wu sp. nov.

Fig. 1C

Type specimens.

Holotype. China • Jiangxi Province, Ganzhou City, Rentian Town (壬田镇), Mianshui River (25.989557°N, 116.131333°E), 13 March 2018, coll. Xiongjun Liu (NCFM180325). Paratypes. Same data as holotype (NCFM180326-NCFM180328).

Diagnosis.

Inversidens rentianensis sp. nov. is morphologically distinct from the other two recognized species within the genus by shell shape, beak position and nacre colour (Table 2 ). Diagnostic characteristics: shell irregularly subtriangular; curvature of the ventral margin slight, nearly straight; umbo situated 1/2 of shell length; nacre reddish.

Description.

Shell irregularly subtriangular, medium thickness, and quite inflated. Anterior margin regularly rounded; ventral margin nearly straight; posterior margin obliquely arc-shaped. Umbo prominent and slightly eroded. Umbo sculptured with feebly wavy wrinkles. Posterior slope formed by the ventral margin and posterior margin low, triangular. Epidermis shining black or with brownish-yellow hue. Only one cardinal tooth in each valve, shape triangular. Laterals thick, a little curved, 2 in each valve. Nacre reddish-bronze in colour.

Length 43-52 mm, height 29-36 mm.

Etymology.

The specific epithet is derived from the type locality, Rentian Town.

Distribution.

The species is known only from Mianshui River, Rentian Town, Ganzhou City, Jiangxi Province, China (present study) (Fig. 2 ).

GenBank accession number.

Holotype, NCFM180325: MZ073336; paratypes, NCFM180326: MZ073337.

Molecular analyses.

Pairwise COI sequence divergences from Inversidens brandtii and Inversidens rentianensis sp. nov. were conducted using MEGA 5.0. Based on the uncorrected p -distance model, the intraspecific divergences of I. brandtii and I. rentianensis sp. nov. were both 0.00%. The interspecific divergence of I. brandtii and I. rentianensis sp. nov. was 10.1%. Both BI and ML trees obtained a completely consistent topology. Consistent topology relationships are shown in Figure 3 . In the phylogenetic trees, I. rentianensis sp. nov. formed a well-supported sister-group relationship with Inversidens brandtii (PP = 1.00, BS = 100; Fig. 3 ). The genera Pronodularia and Inversiunio belong to different clades well-separated from Inversidens (Fig. 3 ).

Remarks.

Species delineation can be problematic in the presence of morphological ambiguities due to phenotypic plasticity and convergence (e.g., cryptic species), especially in mollusks ( Zieritz et al. 2010; Inoue et al. 2013). The use of molecular genetics can aid species delineation in the case of phenotypic plasticity and/or convergence ( Pieri et al. 2018; Wu et al. 2018). Inversidens rentianensis sp. nov. can be distinguished from congeneric species based on diagnostic characteristics of the shell. In this study, we also analyzed the interspecific divergence between Inversidens brandtii and Inversidens rentianensis sp. nov. based on the COI barcode. The results showed that the average interspecific divergence between the two species was 10.1%, which was much higher than intraspecific divergences. Genetic analysis conducted in this study supports I. rentianensis sp. nov. as a valid species, which can be easily distinguished by the COI barcode.

Figures

Figure 1. Photographs of Inversidens taxa A I. brandtii B I. pantoensis C I. rentianensis sp. nov. Photos: [A, B] from the MUSSEL Project, [C] from this study, NCFM 180325 (holotype), scale is 2 cm.

Figure 2. Photograph of sampling site of Inversidens rentianensis sp. nov. in China.

Figure 3. Phylogenetic tree of freshwater mussels inferred from Bayesian Inference (BI) and Maximum Likelihood (ML) analyses of COI barcode. Support values above the branches are posterior probabilities (PP) / bootstrap support (BS). Red font indicates the new species from this study.