Balwantia Prashad, 1919

Bolotov, Ivan N., Sonowal, Jyotish, Kardong, Devid, Pasupuleti, Rajeev, Subba Rao, Nalluri V., Unnikrishnan, Suresh Kumar, Gofarov, Mikhail Y., Kondakov, Alexander V., Konopleva, Ekaterina S., Lyubas, Artem A. & Vikhrev, Ilya V., 2024, Discovery of an endemism hotspot of freshwater mussels (Bivalvia: Unionidae) in Assam, with a description of two new genera, Zoological Journal of the Linnean Society (Zool. J. Linn. Soc.) 202 (4), pp. 1-19 : 13

Genus Balwantia Prashad, 1919

(type species: Anodonta soleniformis Benson, 1836 ; by original designation) ( Prashad 1919).

( Figs 4A , 7B, C )

Differential diagnosis: Balwantia is the sister-lineage of the genus Trapezidens but it cannot be placed in the latter genus due to a combination of specific morphological characters: ultra-elongated, narrow shell (vs. ovate or rhomboid, broad) and reduced pseudocardinal teeth (vs. well-developed, massive). Conchologically, Balwantia resembles other ultra-elongated genera of freshwater mussels such as Solenaia Conrad, 1869 , Sinosolenaia Bolotov et al., 2021 , Lanceolaria Conrad, 1853 , Parvasolenaia Huang and Wu, 2019 , and Koreosolenaia Lee et al., 2020 . External similarity between these genera reflects convergent evolution and most of them cannot be distinguished based on conchological features alone ( Bolotov et al. 2021). Balwantia differs from these genera by having unhooked glochidia and tetragenous brooding mode ( Prashad 1919, Bolotov et al. 2022a).

Comments: The genus is monotypic and contains a single species having an ultra-elongated shell, B. soleniformis ( Table 1 ; Fig. 4A ). Our new phylogenetic results support the morphology-based assumption that this genus belongs to the Parreysiinae due to the presence of unhooked glochidia and tetragenous brooding mode ( Pfeiffer et al. 2021, Bolotov et al. 2022a). We also show that it is a representative of the tribe Lamellidentini , whereas Balwantia was placed as incertae sedis Parreysiinae in our earlier revision ( Bolotov et al. 2022a).

Figures

Figure 4. Shells of Lamellidentini species from Assam (sequenced specimens; outer view of the left valve and inner view of the right valve).A, Balwantia soleniformis (Benson, 1836), sample DLS-DU BS-BDH-1. B–G, Lamellidens jenkinsianus (Benson, 1862): topotypes LJ-NKM-2 (B), LJ-NKM-3 (C), L5-NKM-1 (D), L4-NKM-1 (E), L5-NKM-4 (F), and L4-NKM-2 (G). Scale bars = 10 mm. The shell vouchers of the new samples are deposited in FBRC ZSI and DLS-DU (Supporting Information, Dataset S1). Photos:J.Sonowal and D. Kardong.

Figure 7. Habitats of little-known freshwater mussel species in Assam.A, collecting locality of Assamnaia involuta gen. et comb.nov.: a shallow oxbow lake with silt and clay bottom substrate, Dhansiri River valley, Golaghat, 26 March 2022. B, collecting locality of Balwantia soleniformis, Indonaia corbis, Pseudoscabies scobina gen. et comb.nov., and Parreysia marcens: Burhidihing River, Dibrugarh, 22 February 2022. The white arrow shows the river cliff, whose bottom portion houses numerous B. soleniformis burrows; the river cliff is mostly composed by firm ground (hard clay). C, close-up view of an aggregation of B. soleniformis burrows in the river cliff,22 February 2022. Living mussels were extracted from submerged burrows.Photos: J. Sonowal and D. Kardong.