Pseudoscabies Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao, 2024

Genus Pseudoscabies Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao gen. nov.

(type species: Unio scobina Hanley, 1856 View in CoL ).

( Fig. 3I–K View Figure 3 )

LSID: https://zoobank.org/ urn:lsid:zoobank.org:act:6366F102-F465-4FBD-BFF2-D8BF8FEE87C7

Differential diagnosis: Phylogenetically, the new genus is the sister-lineage of Indonaia . However, it does not correspond to the latter genus by having a specific, strongly-developed sculpture over the shell disc, i.e. V- or W-shaped ridges at the middle of the shell, and waved and arcuate ridges at the anterior and posterior parts of the shell, respectively, while corresponding depressions display the same pattern in the inner side of the shell. Conchologically, the new genus is similar to the genera Harmandia Rochebrune, 1882 and Scabies Haas, 1911 ( Indochinellini ) but could be distinguished from these taxa by having a rectangular V- or W-shaped sculpture at the middle part of the shell. Furthermore, Indonaia rugosa (Gmelin, 1791) remotely resembles the new genus by having a few W-shaped ridges near the umbo but these ridges are less developed, less prominent, and do not spread over the dorsal half of the shell.

Description: Shell thin, rather compressed; anterior margin broadly rounded; posterior margin slightly narrower, with small wing; dorsal margin slightly convex, its posterior part angular, umbo not prominent; ventral margin slightly convex. Umbo slightly shifted to the anterior part of the shell. Periostracum brown, sometimes with green markings on ridges at the posterior half of the shell. Nacre bluish white, sometimes with goldish spots. The shell is covered by peculiar sculpture: repeating V- or W-shaped ridges at the middle of the shell, surrounded by waved ridges at the anterior part of the shell and arcuate ridges at the posterior part of the shell. This sculpture is clearly visible in the inner side of the shell by depressions, the pattern of which corresponds to ridges on the outer side. Pseudocardinal teeth rather short, representing shallow, smooth ridges, two teeth in right valve and one tooth in left valve. Lateral teeth elongated, slightly curved, lamella-like, one tooth in right valve and two teeth in left valve. Anterior adductor muscle scar ovate, shallow; posterior adductor muscle scar ovate or round, very shallow, sometimes weakly visible.

Etymology: The name of this genus comprises of two words: ‘pseudo’ (translingual prefix, meaning ‘appears like a true but is false’) and ‘scabies’ [reference to the genus Scabies , in which it was placed due to a similar shell sculpture ( Subba Rao 1989, Sonowal et al. 2021)].

Distribution: Endemic to the Brahmaputra River basin, north-eastern India.

Habitats: Topotypes of Pseudoscabies scobina gen. et comb. nov. (N = 8 specimens) were collected from the Sesa and Burhidihing rivers in Assam ( Fig. 7B View Figure 7 ). The species was found together with Parreysia marcens , Indonaia corbis , and Balwantia soleniformis .

Comments: Here, we transfer the nominal species Unio scobina Hanley from Indonaia to Pseudoscabies gen. nov. and propose P. scobina gen. et comb. nov.; its conchological form with broadly rounded V-shaped sculpture (e.g. see Fig. 3K View Figure 3 ) was described as Unio radula Hanley, 1856 [= Nodularia (sec. Radiatula) lima Simpson, 1900 ].