Gibbosula sinensis Z. - G. Chen, Y. - T. Dai, H. Chen & X. - P. Wu, 2025

Gibbosula sinensis Z. - G. Chen, Y. - T. Dai, H. Chen & X. - P. Wu sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 5 D View Figure 5

Gibbosula laosensis View in CoL – Guo 2022: 42 (southern Yunnan).

Type material.

Holotype: • NCUMB B 2507001 , Nanbanhe River, a large tributary of the Lancangjiang River [澜沧江支流南班河], upstream of Menglun Town [勐仑镇上游], Xishuangbanna Dai Autonomous Prefecture [西双版纳傣族自治州], Yunnan Province [云南省], China, leg. Z. - G. Chen, Y. - T. Dai, H. - F. Hu, Y. - Y. Zhang, March 2023.

Paratypes: • 18 shells with soft part, 27 paired dead empty shells, 62 single piece dead empty shells. NCUMB B 2507002–011 (soft part stored in alcohol separately), leg. Z. - G. Chen, March 2024, other information same as holotype ; NCUMB B 2507012–019 (soft part kept in shell and stored in formalin), NCUMB B 2507020–045 (paired dead empty shells), ZMNH RS 202501 (paired dead empty shell), NCUMB B 2507047–104 (single piece dead empty shells), ZMNH RS 202502–05 (single piece dead empty shells), other information same as holotype .

Diagnosis.

Shell oblong, slender, very curved, relatively thin, fragile, rather smooth. Front end of the shell higher than the posterior end. Inhabiting the deep torrent of the wide section of the lower Lancangjiang River (upper Mekong River).

Description.

Shell large, symmetric, flat, relatively thin, fragile, sub-glossy, oblong, slender, very curved, rather smooth, dark brown to black. Anterior, dorsal and posterior margin rounded; ventral margin concave. Umbo smooth, inflated, slightly under hinge line, located at 1 / 4 of the dorsal margin, and often eroded. Umbo cavity shallow. Growth lines arranged in irregular concentric circles. Hinge long and strong. Mantle attachment scars small, deep and sparse. Mantle muscle scars obvious. Anterior adductor muscle scars irregular oval, deep and coarse; posterior adductor muscle scars oval, smooth. Left valve with two pseudocardinal teeth, anterior one reduced, posterior one strong and connected to lateral teeth; right valve with two pseudocardinal teeth, anterior one strong and high, posterior one reduced, connected to lateral teeth. Lateral teeth of both valves relatively strong, rough, long and thick. Nacre white, with irregular yellow halo in partial individuals.

Mantle light brown. aperture margins black, papillae of the excurrent aperture highly degraded, papillae of the incurrent aperture strong and forked. Gills light brown, inner gills slightly longer and wider than outer gills. Labial palpsrown, irregular triangle, distally pointed. Visceral mass grayish white. Foot black, fades to brown in formalin.

Measurements.

Holotype: shell length 116.4 mm, height 45.3 mm, width 30.4 mm. Paratypes: shell length 101.9–130.2 mm, height 40.3–49.1 mm, width 27.2–36.0 mm.

Etymology.

The species is made from Latin Sino for China, referring to its type locality. The Chinese vernacular name is 中华弓背蚌 (pīnyīn: zhōng huá gōng bèi bàng) and the English vernacular name is Chinese freshwater pearl mussel.

Distribution and ecology.

Known from several kilometers of the Nanbanhe River upstream of Menglun Town (Fig. 3 View Figure 3 ). Living under huge stone in the deep torrent of the wide river section (Fig. 4 View Figure 4 ). The habitat will not be exposed out of the water even during the season with the lowest water level. Usually found together with Lens comptus (Deshayes, 1876) , Unionetta fabagina (Deshayes, 1876) , and Bineurus mouhotii (Lea, 1863) . The population is extremely small, with fewer than 100 living animals found in a 3 - year survey. The reproduction of the new species has encountered serious problems, the population is almost entirely composed of elderly individuals and with no juveniles. It will soon become extinct without protective measures.

Remarks.

The new species was misidentified as G. laosensis by Guo (2022). Guo (2022) vaguely recorded the distribution of “ G. laosensis ” in China as southern Yunnan, which is actually the type locality of the new species.