Namkongnaia inkhavilayi, Jeratthitikul & Sutcharit & Ngor & Prasankok, 2021

Jeratthitikul, Ekgachai, Sutcharit, Chirasak, Ngor, Peng Bun & Prasankok, Pongpun, 2021, Molecular phylogeny reveals a new genus of freshwater mussels from the Mekong River Basin (Bivalvia: Unionidae), European Journal of Taxonomy 775, pp. 119-142 : 130-132

Namkongnaia inkhavilayi gen. et sp. nov.

urn:lsid:zoobank.org:act:622F7788-F0A4-449D-814A-5B49CD20B228

Figs. 3 , 4A–B ; Tables 1 , 3

Pilsbryoconcha lemeslei – Brandt 1974: 263, pl. 18 fig. 22 (in part, only records from “Nang Rong (Prov. Burirum)”, Thailand) [non Anodonta lemeslei Morelet, 1875 ].

Etymology

This new species is dedicated to our colleague and distinguished malacologist, Dr Khamla Inkhavilay, from the National University of Laos.

Type material

Holotype LAOS • Kammoune Province , Bunghona Market, 7 km N of Xe Bangfai River; 17.13674° N, 104.98591° E; E. Jeratthitikul, K. Wisittikoson, A. Fanka, N. Wutthituntisil and P. Prasankok leg.; sold by local people; MUMNH-UNI2831 .

Paratypes LAOS • 5 shells; same collection data as for holotype; MUMNH-UNI2832 to UNI2835 .

Other material

LAOS • 2 shells; Nong Njang , N of Vientiane; R. Brandt leg.; BMNH-MP-D262 • 1 shell; Nong Bua Thong near Vientiane; R. Brandt leg.; ANSP-H19043 • 2 shells; Nong Bua Thong near Vientiane; R. Brandt leg.; MCZ-280932 • 2 shells; Nong Bua Thong near Vientiane; R. Brandt leg.; SMF-258771 • 2 shells; Nong Bua Thong , Vientiane; R. Brandt leg.; SMF-319294 • 1 shell; Bang Jian near Vientiane; R. Brandt leg.; ANSP-H19044 • 6 shells; Nang Njang near Vientiane; MNHN-MP-3154 • 4 shells; Nang Njang near Vientiane; R. Brandt leg.; MNHN-MP-3157 • 3 shells; swamp near Pakse; R. Brandt leg.; SMF-225743 .

THAILAND • 1 shell; Nakhon Phanom, Tha Uthen, Tha Uthen, Thuai River ; 17.56221° N, 104.60890° E; E. Jeratthitikul, K. Wisittikoson and P. Prasankok leg.; MUMNH-UNI2706 • 1 shell; Sakon Nakhon, Sawang Daen Din, Bong Tai, Songkhram River ; 17.39570°N, 103.30048°E; E. Jeratthitikul and K. Wisittikoson leg.; MUMNH-UNI0318 • 1 shell; Buriram, Nang Rong, Huai Tadjek ; R. Brandt leg.; USNM-786219 • 1 shell; Buriram, Nang Rong, Huai Tadjek ; R. Brandt leg.; SMF-220822 • 4 shells; Buriram, Nang Rong; SMRL-2662 • 1 shell; Buriram, Huai Ta Djek near Nang Rong; ANSP-H19042 .

Description

Shell medium-sized, length 80.9–102.2 mm, height 26.2–37.2 mm, width 13.6–19.1 mm ( Table 3 ). Shell rather thin, narrow and elongated (H/L ratio = 0.32–0.36), very inequilateral, compressed. Dorsal margin straight, anterior at the same level as posterior. Umbonal area eroded, not elevated. Anterior margin round; posterior margin elongated and rounded. Ventral margin almost straight, slightly curved upward posteriorly. Posterior ridges low, wide and obtuse, not prominent. Periostracum thin, greenish to dark brown, the eroded part coppery-brown. Shell surface with fine growth lines. Ligament very narrow. Hinge without dentition, posterior end of the hinge structure with V-shaped fossette. Anterior adductor muscle scar placed relatively far from the dorsal margin, shallow, ovate, fused with pedal retractor muscle scars; posterior adductor muscle scars very shallow, almost invisible. Pallial line very faint. Nacre whitish with cream tint near the umbo. Excurrent aperture smooth, shorter than incurrent. Incurrent with 1–2 rows of conical papillae, varying in length. Small epithelial folds form a fused bridge separating excurrent and incurrent aperture. Gills elongated and slightly ribbed. Anterior margin of inner gills slightly longer and wider than that of inner outer gills. Glochidia unknown.

Distribution

This new species appears to occur in the Lower Mekong watershed. In Laos, it was recorded from several locations near Vientiane, Kammoune, and Champasak Provinces. In Thailand, it is known from the Songkram and Mun river basins in the northeast region ( Brandt 1974).

Habitat

Specimens of the new species were bought on a local market near the Xe Bangfai River. However, specimens from the Thuai and Songkhram Rivers in Thailand were found buried in the mud substrate of still water. Brandt (1974) also reported ponds as a general habitat of this species.

Remarks

The specimens recorded by Brandt (1974) from Nang Rong, Buriram, Thailand (SMF-220822) show a shorter but wider shell and a relative rounded ventral margin. In addition, although the hinge area of this species has no dentition, the trace of a rudimentary pseudocardinal tooth is seen as a very tiny tubercle in some individuals.

Figures

Fig. 3. Map showing distribution localities of Namkongnaia gen. nov. Boundaries of river basins follow Abell et al. (2008).

Fig. 4. Namkongnaia inkhavilayi gen. et sp. nov. A. Holotype MUMNH-UNI2831. B. Paratype MUMNH-UNI2836, both from the type localty in Xe Bangfai River, Kammoune Province, Laos. Scale bars: 10 mm.