Digoniostoma iravadica (Blanford, 1869) comb. nov.

Bithynia iravadica Blanford, 1869: 446 (Myanmar, Mandalay, Ava, swamp, and river); Molluscabase, 2021: taxon inquirendum.

D. iravadica – Rao, 1989: no description or remarks, only figures with ambiguous genus assignment and species name, figs 122–123.

Diagnosis.

Shell big, thin, high spiral whorls, thin outer lip, base of peristome angled, umbilicus narrow and deep, penial appendix about one-third of distal part of penis in length.

Material examined.

• 7 specimens preserved in ethanol, Shan State, Taunggyi District, Shwenyaung, Taung Lay Lone, a shallow pond in the north of town (Fig. 1 B. a), 20°44'56.7"N, 96°53'59.4"E, 6 Jul. 2024, Le-Jia Zhang leg., KIZ.2400076 –2400082 • 1 dry shell specimen, Mandalay Region, Meiktila, Wundwin, Seywa, dry pond near road, 21°14'15.2"N, 95°50'27.7"E, 29 Jun. 2024, Le-Jia Zhang leg., KIZ.2400083 .

Description.

Shell (Fig. 11) relatively large for the family (Table 1), thin and fragile, high conical, pale olive green to grey, with 5.5 whorls at adulthood; teleoconch high, relatively smooth but with very fine grid-like micro-structure, without shoulder; aperture ovate, nearly half of shell in height, outer lip thin, inner lip straight, base of peristome angled; umbilicus narrow and deep, always open obviously, with a keel around.

Operculum (Figs 11 A, G, 4 A) calcium, ovate, thin, slightly smaller than aperture, transparent grey; exterior surface smooth, with obviously concentric growth lines, nucleus close to the inner opercular margin; interior surface with many vermicular veins covering most parts of inner opercular region, and a few concentric veins on the margin of inner opercular region.

Penis (Fig. 5 C) with a white penial appendix located close to the base of penis, penial appendix about one-third of distal part of penis in length.

Radula (Fig. 12) taenioglossate; central tooth upper margin with one long triangle central cusp and four small sharp cusps on either side, lateral margin each with three small sharp cusps; lateral tooth with one long triangle central cusp and four small sharp cusps; inner marginal tooth with 10 to 11 small cusps; outer marginal tooth with 10 small cusps.

Remarks.

This species can be distinguished from other Digoniostoma species based on high spiral whorls, fine grid-like micro-structure shell surface, narrow umbilicus, and very long distal part of the penis. The molecular study also confirms the validity of this species. The radula of Digoniostoma iravadica has the central cusp with a different shape and a larger number of small sharp cusps on both the central tooth and the lateral tooth, compared to that of Hydrobioides species from Inle Lake.

Habitat and distribution.

Rivers, swamps, and shallow ponds in central Myanmar (Mandalay, Meiktila, Taunggyi).