Diaurora laeve Chen, Dai, Huang & Wu, 2023

Chen, Zhong-Guang, Dai, Yu-Ting, Ouyang, Shan, Huang, Xiao-Chen & Wu, Xiao-Ping, 2023, Unveiling the identity of Diaurora Cockerell, 1903 (Bivalvia, Unionidae): morphology, molecular phylogenetics, and the description of a new species, ZooKeys 1173, pp. 131-144 : 131

Diaurora laeve Chen, Dai, Huang & Wu sp. nov.

Figs 3B , 4B , 5B

Type material.

Holotype: 22_NCU_XPWU_DL01, Zishui River [资水], Shaoyang County [邵阳县], Shaoyang City [邵阳市], Hunan Province [湖南省], China, 26°59′27″N, 111°16′10″E, collected by Zhong-Guang Chen & Zheng-Jie Lou in November 2022; Paratypes: 22_NCU_XPWU_DL02-100, other information same as holotype.

Diagnosis.

Shell reniform. Periostracum with irregular broken blackish-green rays. Zigzag sculpture only presented in umbo area.

Description.

Shell (Figs 3B , 4B ). Shell small size, symmetric, solid, moderately thick, sub-glossy, reniform. Anterior margin oval, inflated; dorsal margin curved downwards and truncate; ventral margin slightly rounded or nearly straight; posterior margin oval. Umbo inflated, above hinge line, located at 1/3 of the dorsal margin, and often eroded. Periostracum orangish to brownish, with irregular broken blackish-green rays and thin growth lines. Growth lines arranged in irregular concentric circles. Zigzag sculpture only presented in umbo area. Hinge short. Ligament short and strong. Mantle muscle scars obvious. Anterior adductor muscle scars oval, deep, smooth in junior but rough in adult; posterior adductor muscle scars long oval, smooth. Left valve with two pseudocardinal teeth, equal height, anterior tooth small and flat, posterior tooth thick and pyramidal; anterior pseudocardinal tooth of the right valve well developed, posterior pseudocardinal tooth reduced, connected to lateral teeth. Lateral teeth of both valves long and thick. Nacre light orangish.

Holotype: length 41.8 mm, height 29.1 mm, width 17.0 mm; Paratypes: length 27.4-45.0 mm, height 17.6-30.8 mm, width 11.0-17.6 mm.

Soft anatomy (Fig. 5B ). Mantle off-white to light-brownish, aperture margins brown, flap margin with yellowish papillae. Gills light-brownish, inner gills slightly longer and wider than outer gills. Labial palps yellowish to brown, distally pointed and irregularly fan-shaped in appearance. Visceral mass creamy white, foot orange.

Etymology.

The specific name laeve is made from the Latin laeve for smooth, an adjective, alluding to the smoother shell surface of this species.

Vernacular name.

平滑金黄蚌 (Pinyin: ping hua jin huang bang).

Distribution and ecology.

Diaurora laeve sp. nov. is known from the type locality only (Fig. 6 ). It was found to occur in a pebbly substrate of the river together with Nodularia douglasiae and Lanceolaria triformis (Fig. 7 ). It is the dominant species in the habitat, accounting for 98% of the total density of freshwater mussels.

Remarks.

The placement of the new species in Diaurora is supported by both morphology and molecular phylogenetic analysis. Diaurora laeve sp. nov. can be easily distinguished from D. aurorea by its reniform shell, smaller zigzag sculptured area, and irregular rays on the shell. The different habitat preferences of Diaurora laeve sp. nov. and D. aurorea may have led to their differentiation. Diaurora aurorea is commonly found in the middle reaches of sandy substrate tributaries, while Diaurora laeve sp. nov. prefers to inhabit the upper reaches of pebbly substrate tributaries. In recent years, with more in-depth investigations and field surveys, new freshwater mussel species such as Inversidens rentianensis Wu & Wu, 2021 and Pseudocuneopsis sichuanensis Huang, Dai, Chen & Wu, 2022 have been discovered in small tributaries of China ( Wu et al. 2021; Wu et al. 2022). These findings suggest that the diversity of freshwater mussels in small tributaries of China remains to be fully explored, and future extensive exploration may lead to the discovery of other yet-to-be-described species.

Figures

Figure 3. Specimens of Diaurora and Acuticosta chinensis A Diaurora aurorea, 22 _ NCU _ XPWU _ DA 03 B Diaurora laeve sp. nov., holotype: 22 _ NCU _ XPWU _ DL 01 C Acuticosta chinensis, 22 _ NCU _ XPWU _ AC 01.

Figure 4. Comparison of the radial pattern on the shell surface in Diaurora A Diaurora aurorea, 22 _ NCU _ XPWU _ DA 04 B Diaurora laeve sp. nov., 22 _ NCU _ XPWU _ DL 02.

Figure 5. Soft anatomical characters of Diaurora A Diaurora aurorea, 22 _ NCU _ XPWU _ DA 15 B Diaurora laeve sp. nov., 22 _ NCU _ XPWU _ DL 50. aam, anterior adductor muscle; pam, posterior adductor muscle; ea, excurrent aperture; ia, incurrent aperture; pia, papillae of the incurrent aperture; pea, papillae of the excurrent aperture; ig, inner gills; og, outer gills; m, mantle; lp, labial palps; vm, visceral mass; f, foot.

Figure 6. Distribution map of Diaurora. Star: type locality of Diaurora laeve sp. nov.; solid triangle: type locality of Diaurora aurorea; hollow triangle: new locality of Diaurora aurorea.

Figure 7. Habitat of Diaurora. A habitat of Diaurora aurorea, Fuhe River, Fuzhou City, Jiangxi Province, China B habitat of Diaurora laeve sp. nov., Zishui River, Shaoyang City, Hunan Province, China.