Mekongia Crosse & P. Fischer, 1876

Zhang, Le-Jia & von Rintelen, Thomas, 2021, The neglected operculum: a revision of the opercular characters in river snails (Caenogastropoda: Viviparidae), Journal of Molluscan Studies 87 (2), pp. 1-14 : 12

Mekongia Crosse & P. Fischer, 1876

Examined species: Mekongia jullieni (Deshayes, 1876) ( Figs 2L , 3L , 6L ).

Remarks: Mekongia is not a monophyletic group according to two recent molecular systematic studies (Hirano et al., 2019a; Stelbrink et al., 2020). Here, we only examined the type species of Mekongia , M. jullieni . Mekongia can be distinguished from the other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a nucleus very close to the inner margin, an inner enamel region that is very narrow in width, a large inner opercular region and a relatively small nuclear region with fine shiny grains.

Figures

Figure 2. Exterior surface of opercula of the viviparid species studied. A. Lioplax subcarinata. B. Campeloma decisum. C, D. Callinina georgiana. E. Callinina intertexta. F. Tulotoma magnifica. G. Riƌularia auriculata. H. Amuropaludina praerosa. I. Viƌiparus ƌiƌiparus. J, K. Viƌiparus contectus. L. Mekongia jullieni. M. Tchangmargarya multilabiata. N. Tchangmargarya yangtsunghaiensis. O. Cipangopaludina nagaensis. P. Cipangopaludina crassibuca. ƍ. Cipangopaludina chinensis. R. Margarya melanioides. S. Heterogen longispira. T. Heterogen japonica. Scale bar: 5 mm.

Figure 3. Interior surface of opercula of the viviparid species studied. A. Lioplax subcarinata. B. Campeloma decisum. C, D. Callinina georgiana. E. Callinina intertexta. F. Tulotoma magnifica. G. Riƌularia auriculata. H. Amuropaludina praerosa. I. Viƌiparus ƌiƌiparus. J, K. Viƌiparus contectus. L. Mekongia jullieni. M. Tchangmargarya multilabiata. N. Tchangmargarya yangtsunghaiensis. O. Cipangopaludina nagaensis. P. Cipangopaludina crassibuca. ƍ. Cipangopaludina chinensis. R. Margarya melanioides. S. Heterogen longispira. T. Heterogen japonica. Scale bar: 5 mm.

Figure 6. Shells of the viviparid species studied. A. Lioplax subcarinata. B. Campeloma decisum. C, D. Callinina georgiana. E. Callinina intertexta. F. Tulotoma magnifica. G. Riƌularia auriculata. H. Amuropaludina praerosa. I. Viƌiparus ƌiƌiparus. J, K. Viƌiparus contectus. L. Mekongia jullieni. M. Tchangmargarya yangtsunghaiensis. N. Tchangmargarya multilabiata. O. Cipangopaludina nagaensis. P. Cipangopaludina crassibuca. ƍ. Cipangopaludina chinensis. R. Margarya melanioides. S. Heterogen longispira. T. Heterogen japonica. Scale bar:10 mm.