Rhombuniopsis heres Neumayr, 1899

Fig. 7A–I

Unio heres Neumayr (1899): 644, pl. 1, fig. 6 [‘Lake Tali’ = Lake Erhai, Dali City, Yunnan Province, China]; Simpson (1914): 723 –724.

Rhombuniopsis heres Moskvicheva & Starobogatov (1973): 25, fig. 2.

Material examined. Museum materials. Inst. Zool., Chinese Academy of Sciences, IZCAS: FM 29549. Newly collected material. Adult shell: Lake Jianhu, Diannan Town (Oi 南Dz), 26.478761°N, 99.924064°E, 2021.7 KIZ1904401 – KIZ1904420), collected by Hong Quan Xiang; Lake Chenghai, Chenghai Town, 26.623269°N, 100.651957°E, 2020.5 (KIZ1904421 – KIZ1904423), collected by Hong Quan Xiang; Lake Erhai, Yinqiao Town (ȇėDz), 25.738285°N, 100.172526°E, 2022.7. (KIZ1904424), collected by Zi Bing Yang.

Diagnosis. Shell square or ovate, periostracum dark brown to black; a small number of individuals left and right valve pseudocardinal teeth not obvious.

Description. Shell (Fig.7 A–F). Length 35–80 mm. Shell small, square-shaped or ovate, periostracum shining black or yellow, shell surface smooth, shell symmetrical, of medium thickness; some individuals with distinct posterior ridges, umbo often eroded, ligament short. Anterior adductor muscle scar ovate, very deep; posterior adductor muscle scar round to ovate, shallow; left valve with two pseudocardinal teeth, anterior tooth rather thick, posterior tooth thin; pseudocardinal tooth of the right valve well developed, most individuals have a closed groove in the middle of the pseudocardinal tooth of the right valve, and a small number of individuals have reduced teeth, nacre white.

Comparison. This species can be differentiated from the most similar species R. songmeng sp. nov. in having relatively deeper posterior adductor muscle scars and nacre without lines.

Taxonomic remarks. Neumayr (1899) described Unio heres based on shell samples collected from Lake Erhai. Haas (1920) considered that U. heres should be classified under Rhombuniopsis. The difference between this species and R. superstes has been explained above. Furthermore, it should be noted that Lake Jianhu was connected to Lake Erhai in the past, providing further evidence to support our conclusion. In September 1997 (Inst. Zool., Chinese Academy of Sciences IZCAS: FM 29549), the Chinese Academy of Sciences collected specimens of Pseudodon chaperi (Morgan, 1885) (currently known as Pseudodon vondembuschianus (Lea, 1840)) from Lake Jian. Pseudodon vondembuschianus is widely distributed in Indochina, the Malay Peninsula, Sumatra, Java, and Borneo. Its distribution does not cover Lake Erhai, and no species of the genus Pseudodon has been found in Yunnan. The photographs and descriptions of the shells recorded at that time confirm that they belong to R. heres. Huang & Zhang (1990) collected specimens of the same species from Lake Erhai, but misidentified it as Afroparreysia hunanensis (Haas, 1910) [But this species does not exist. We believe what he meant to say is Acuticosta ovata (Simpson, 1900).], and misspelled the name. We have re-evaluated the photographs of the species and confirmed that it is indeed R. heres. Although Nodularia continentalis (Haas, 1910) shares some conchological similarities with R. heres, the latter species has more prominent pseudocardinal teeth, and its type locality is situated in Hunan. Therefore, we consider them as distinct species.

Habitat and distribution. Lives on muddy to sandy substrates, mostly near rivers emptying to lakes, always at depths of 0–5 m. It is known to occur in the Erhai, Jianhu, Chenghai lakes, as well as in lakes near Lijiang City.