Namkongnaia, 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 : 128-129

Genus Namkongnaia gen. nov.

urn:lsid:zoobank.org:act:77AD43CF-83EC-42B8-B021-A950D4E701A0

Type species

Namkongnaia inkhavilayi gen. et sp. nov., by present designation.

Differential diagnosis

The new genus is distinguished from other genera in Pseudodontini by having a narrow, elongated, and less inflated shell. It is also represented as a distinct clade in multi-locus phylogenetic analyses.

Description

Shell Medium-sized, thin, narrow and elongated, rather compressed, very inequilateral; anteriorly round; posteriorly round or somewhat pointed; umbonal area not elevated and usually eroded. Ligament very narrow. Hinge without dentition, posterior end of the hinge structure with V-shaped fossette. Anterior adductor muscle scar shallow, ovate, and fused with pedal retractor muscle scars; posterior adductor muscle scar very shallow. Excurrent aperture smooth, shorter than incurrent; incurrent with 1-2 rows of conical papillae. Gills elongated and slightly ribbed; anterior margin of inner gills slightly longer and wider than outer gills.

Etymology

The generic name “ Namkongnaia ” is from the word “Namkong”, a name for the Mekong River used by Thai and Lao peoples, and Greek word “naiad” meaning freshwater mussels. The name of this genus thus means “freshwater mussels from Mekong River”.

Distribution

Mekong River and its tributaries in Laos, Cambodia, and Thailand ( Fig. 3 ; Brandt 1974; Ng et al. 2020). The distribution range may include the Mae Klong River Basin in Thailand ( Brandt 1974), although the taxonomic status of the specimens recorded in Brandt (1974) needs to be confirmed.

Remarks

The new genus is currently composed of two species, which are confirmed by our multi-locus molecular data. Other potential species are probably among those previously recognized under the name ‘ Pilsbryoconcha lemeslei ’ by Brandt (1974). This includes the specimens from ‘Bang Pae’, Mae Klong River Basin, Ratchaburi Province (USNM-786217, SMF-BR2663, and ANSP-H19041). These specimens show elongate and narrow shell, which are diagnostic characters of the genus, but differ from other species by having a minute concave ventral margin, and truncated posterior margin with a pointed posterior end. Further examination of fresh materials and DNA investigation would confirm the taxonomic status of these populations.

Figures

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