Pseudobaphia banggiangensis, Bogan & Do, 2018

Bogan, Arthur E. & Do, Van Tu, 2018, An overlooked new species of freshwater bivalve from northern Vietnam (Mollusca: Bivalvia: Unionidae), Raffles Bulletin of Zoology 66, pp. 78-86 : 80-85

Pseudobaphia banggiangensis new species

( Figs. 3 , 4 , 5 , 6 , 7 )

Diagnosis. Pseudobaphia banggiangensis new species is distinguished from other unionid species by the following characters: rather thick shell, inflated, slightly rectangular to oval shell outline, well developed pseudocardinal teeth with nodules extending posteriorly, but not over whole of interdentum, well developed lateral teeth, periostracum smooth, posterior ridge smooth, umbo sculpture consisting of a series of parallel bars, often eroded. Soft anatomy is unknown.

Description. Shells examined reach approximately 70 mm in total length, shell shape slight rectangular to oval in outline, inflated, anterior shell margin evenly rounded, dorsal shell margin nearly straight, ventral margin broadly rounded, posterior margin rather straight or almost squared off, posterior ridge rounded, posterior slope smooth, umbo area inflated, umbo sculpture a series of parallel bars in one specimen with an early bar breaking up into three elongate pustules followed by parallel bars continuing down onto the disk, periostracum reddish brown to dark brown, shell surface smooth lacking any sculpture. Pseudocardinal teeth in right valve with one peg-like, striated pseudocardinal tooth anterior of the umbo, one long, straight lateral tooth, left valve with two striated or sculptured large pseudocardinal teeth extending posteriorly into the interdental area under the umbo and two straight well-developed lateral teeth. Anterior adductor muscle scar deep, smooth and impressed, pedal protractor muscle scar separate, anterior pedal retractor muscle scar united with the anterior adductor muscle scar, posterior adductor muscle scar very faint, pallial line impressed anteriorly, fading posteriorly, umbo cavity open, rather deep, nacre color white becoming bluish iridescent toward posterior margin.

Holotype. Institute of Ecology and Biological Resources ( IEBR), Vietnam Academy of Science and Technology , Hanoi. IEBR-MO1 , Fig. 3 . No collector known.

Paratypes. NCSM 102866 , 2 unpaired valves; Biology Department, Vietnam National University, University of Science , Hanoi, MB-015 K60, 10 unpaired valves. No collector known ( Figs. 4 , 5 , 6 ) ( Table 1) .

Type locality. This species is known only from the Bằng River, Cao Bằng Province, Vietnam. The Bằng River is a

headwater tributary of the Zhu Jiang (Pearl River) draining into the South China Sea in southeast China. The specimens were collected in February 1971. No collector was recorded ( Figs. 3 , 4 , 5 , 6 ).

Comparison with similar species. Pseudobaphia banggiangensis new species does not resemble any other species found in Vietnam with an oval shell shape, very inflated shell and a smooth shell surface with a dark periostracum. Sinanodonta jourdyi has a thin shell and lacks any hinge teeth. Cristaria plicata is thinner shelled, often with posterior dorsal plications and lacks pseudocardinal teeth and has a long thin, lateral tooth. Aculamprotula , Gibbosula , and Lamprotula species are thick shelled, but not as inflated and typically have some plications or pustules on the surface with well-developed hinge teeth. Pseudobaphia banggiangensis new species was originally identified as Protunio messageri ( Fig. 1 ), but that species is rectangular, and has surface sculpture, which is lacking in P. banggiangensis new species. This new species resembles the shell shape, inflation, smooth shell and lack of external sculpture and well developed pseudocardinal teeth with numerous nodules on the hinge plate anterior to the lateral teeth as in Pseudobaphia biesiana ( Fig. 2 ). But, P. banggiangensis new species ( Figs. 3 , 4 , 5 ) differs by having well developed, long lateral teeth unlike the reduced or feeble lateral teeth in P. biesiana ( Fig. 2 ).

Distribution. This species is known only from the Bằng River, Cao Bằng Province, Vietnam ( Fig. 7 ) (Do et al., in press).

Habitat and biology. No notes or information were included with the IEBR or Hanoi University of Science, Museum of Biology specimens. All examined specimens are dry shells and no soft tissues have been preserved.

Conservation status. The specimen label stated the date of collection was February 1971 ( Fig. 6 ). This species has not been reported or collected since 1971. During discussions with local farmers and mussel sellers in local markets in Cao Bằng Province, they do not remember seeing this species. We have not found any evidence this species has been collected in the last 46 years. It is either extremely rare, but more likely presumed extirpated in Vietnam, but we lack any information on the rest of the Pearl River basin in China. Other freshwater mussel taxa reported from Cao Bằng Province that are considered at least extirpated from Vietnam include Lamprotula bazini ( Heude, 1877) and Lamprotula blaisei ( Dautzenberg & Fischer, 1905) (Do et al., in press). Until last year, Gibbosula crassa ( Wood, 1815) was considered extirpated in Vietnam until it was rediscovered in a very short reach of the Bằng River, Cao Bằng Province ( Bogan & Do, 2016). Extinction of freshwater mussels around the world is increasing ( Bogan, 2008; Lydeard et al., 2004; Tedesco et al., 2014) and has been attributed to various causes including: deforestation and effects on rivers, dams and reservoirs, mining, pollution, etc. (e.g., Vaughn & Taylor, 2001; Lydeard et al., 2004; Bogan, 2008; Meyfroidt & Lambin, 2008; Strayer & Dudgeon, 2010).

Etymology. The species is named for the Bằng River in Cao Bằng Province, Vietnam, where the species was collected.

Comparative material examined. No additional specimens outside of those in Hanoi were found. Figures of Pseudobaphia biesiana from Haas (1910 –1920), He & Zhuang (2013) and Graf & Cummings (2017) were compared with the type series of P. banggiangensis new species.

Figures

Fig. 3. Outside of the right valve and inside of the left valve of the holotype of Pseudobaphia banggiangensis new species. IEBR-MO1, length 70.5 mm; height 48.0 mm; width 32.0 mm.

Fig. 4. External view of the Paratype Lot MB-015-K60, of Pseudobaphia banggiangensis new species, previously identified as Protunio messageri in the Vietnam National University, Hanoi University of Science, Biology Department, Museum of Biology, Hanoi, Vietnam.

Fig. 5. Internal view of the Paratype Lot MB-015-K60, of Pseudobaphia banggiangensis new species, previously identified as Protunio messageri in the Vietnam National University, Hanoi University of Science, Biology Department, Museum of Biology, Hanoi, Vietnam.

Fig. 6. Printed label and original label with lot MB-015-K60 misidentified as Protunio messageri from Sông Bằng Giang, Cao Bằng, February 1971 with 9 specimens [10 valves in lot]. Biology Department, Vietnam National University, University of Science, Hanoi.

Fig. 7. Map of the distribution of Pseudobaphia banggiangensis new species (Do et al., in press).

Fig. 1. Protunio messageri MCZ 210114.

Fig. 2. Unio biesianus Heude, 1877. Heude, 1877: plate 14, figure 30.