Heterogen Annandale, 1921

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

Heterogen Annandale, 1921

Examined species: Heterogen longispira (E. A. Smith, 1886) ( Figs 2S , 3S , 6S ); Heterogen japonica (Martens, 1861) ( Figs 2T , 3T , 6T ).

Remarks: Heterogen longispira has always been considered as the only species of the genus Heterogen , which is endemic to Lake Biwa, Japan. Recently, ‘ Cipangopaludina ’ japonica has also been assigned to the genus on the basis of molecular systematic data (Hirano et al., 2019a); the opercular characters of this species also match those of H. longispira , including a relatively large, smooth and shiny nuclear region and a thin marginal region. The combination of these opercular characters differs from those found in other viviparid genera with a concentric inverted-comma-shaped operculum.

The operculum of H. japonica is clearly higher than it is wide, while in H. longispira the opercular height and width are roughly the same. In addition, H. longispira has a larger inner opercular region as compared with H. japonica .

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.