Rhombuniopsis fultoni Moskvicheva & Starobogatov, 1973

Fig. 5A–D

Rhombuniopsis fultoni Moskvicheva & Starobogatov (1973): 24, fig. 2 [‘ Yunnan fu’=Kunming, Yunnan Province, China]; Graf & Cummings (2007): 304; He & Zhuang (2013): 102, Figs 239–240; Zieritz et al. (2018): 29 –44; Graf & Cummings (2021): 15; Liu et al. (2022): 1 –37.

Material examined. Newly collected material. Adult shell: Lake Lulianghai, Zhongshu Town (中NJDz), 25.028233°N, 103.689557°E, 2022.1. (KIZ1904201 – KIZ1904210), collected by Hong Quan Xiang and Yue Ming He; Lake Dianchi, Haikou (DZ口), 24.782123°N, 102.610330°E, 2022.1. (KIZ1904211), collected by Yi Feng Liu; Lake Dianchi, Haikou (DZ口), 24.78012°N, 102.62258°E, 2023.5. (KIZ1904212 – KIZ1904217), collected by Hong Quan Xiang.

Diagnosis. Shell rounded or nearly rounded, dark brown to black, ventral margin rounded, umbo with wavy wrinkles.

Description. Shell length 20–25 mm. Shell small, inflated, solid, symmetrical, rounded or nearly rounded. Anterior and posterior margins oval, ventral margin rounded; the umbo sometimes sculptured with wavy wrinkles, often eroded. Ligament short; growth lines arranged in concentric circles; dorsal outline arched smoothly. Periostracum shining black or greenish-yellow, smooth; left valve with two pseudocardinal teeth, anterior tooth rather thin, posterior tooth thick; anterior pseudocardinal tooth of the right valve well developed, spherical, posterior tooth sometimes connected to lateral teeth; nacre white.

Comparison. This species can be differentiated from the most similar species R. linan sp. nov. by having a rounder shell with relatively smaller pseudocardinal teeth and fewer wavy wrinkles near the umbo.

Taxonomic remarks. According to Moskvicheva and Starobogatov (1973), Rhombuniopsis fultoni was described based on shells collected from Yunnan (type locality: Kunming, China). He and Zhuang (2013) provided specimen images from Lake Dianchi in Kunming. Based on comparative descriptions, we believe they represent the same species. Huang & Zhang (1990) described a new species found in Dianchi, Unionea ovatiquadreta (Huang & Zhang, 1990) . However, after searching for Huang & Zhang’s information from the relevant years, we could not find any images of that species. Other references citing this species also did not provide any relevant literature. We consider this species to be invalid. Therefore, we can only speculate that it is R. fultoni based on the shape described in its name and its place of origin. In addition, Huang & Zhang (1990) recorded ‘ Unionea fagana ’ from Dianchi. According to our research, this name should actually be a misspelling of Unionetta fabagina (Deshayes & Jullien, 1876) . Based on our field investigations in Dianchi, we believe that Huang & Zhang’s identification was wrong, and this species should actually be R. fultoni .

Habitat and distribution. Lives on muddy to sandy substrates, mostly found near rivers leading to lakes, always at depths of 0–3 m in Lake Dianchi, Lulianghai and lakes near Qujing City.