Digoniostoma Annandale, 1920

Digoniostoma Annandale, 1920 in Annandale & Seymour Sewell (1920): 103 –104; Starobogatov, 1970: 26; Izzatullaev, 1982: 336–340; Rao, 1989: 79–80; Ng & Tan, 2024: 154–155.

Bithynia (Digoniostoma) – Brandt, 1974: 58; Ramakrishna, 2007: 118–122; Glöer & Bössneck, 2013: 137–156.

Bithynia – Molluscabase, 2024 b: synonym.

Type species.

Paludina cerameopoma Benson, 1830 (original designation).

Diagnosis.

Shell large for the family, thin and fragile, inner lip straight, base of peristome angled, umbilicus open, usually with a keel around; penial appendix located close to the base of penis, penial appendix much shorter than distal part of penis.

Remarks.

This genus is always considered as a subgenus or even a synonym of Bithynia by some recent studies, e. g., Glöer and Bössneck (2013) and Molluscabase (2024 b). However, the molecular study has confirmed that Digoniostoma from South and Southeast Asia is a distinct group and not closely related to Bithynia, mainly from Europe. Morphologically, this genus also can be easily distinguished from other bithyniid groups based on large shell with base of peristome angled and open umbilicus with a keel around. Molecular, morphological, and distributional evidence all support that Digoniostoma is a valid genus. There are 11 species and subspecies assigned to this genus based on molecular evidence and former morphological studies: Digoniostoma cerameopoma (Benson, 1830); Digoniostoma funiculata (Walker, 1927), stat. nov.; Digoniostoma kashmirense (G. Nevill, 1885); Digoniostoma lithoglyphoides Nesemann & Sharma, 2007; Digoniostoma oxiana Izzatullaev, 1982; Digoniostoma pulchella (Benson, 1836); Digoniostoma iravadica (Blanford, 1869); Digoniostoma siamensis siamensis (Lea, 1856), stat. nov.; Digoniostoma siamensis goniomphalos (Morelet, 1866) stat. nov.; Digoniostoma textum Annandale, 1921; Digoniostoma truncatum (Eydoux & Souleyet, 1852) . The taxonomy of Digoniostoma species, especially the species from India, should be revised.