Filopaludina Habe, 1964

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 : 11-12

Filopaludina Habe, 1964

Examined species: Filopaludina martensi (Frauenfeld, 1864)

( Figs 4M , 5M , 7M ); Filopaludina bengalensis (Lamarck, 1822) ( Figs 4N , 5N , 7N ); Filopaludina gigantea (von dem Busch, 1843) ( Figs 4O , 5O , 7O ); Filopaludina luzonica (Kobelt, 1909) ( Figs 4L , 5L , 7L ).

Remarks: The opercular characters of Filopaludina are broadly similar to those of Idiopoma . Notably, both show an inner opercular region almost completely covered by a sandpaper-like layer. However, in Filopaludina , this layer and the inner opercular region are maroon coloured, whereas in Idiopoma they are brownish yellow. In addition, the enamel region of Filopaludina lacks the fine grid-like pattern found in the enamel region of Idiopoma .

The operculum of F. martensi differs from that of the other examined species of Filopaludina : it has a relatively small inner opercular region that is almost completely covered by a sandpaper-like layer, with many radial veins; is almost as high as it is wide; and has a notably convex outer margin.

The opercula of F. bengalensis and F. gigantea are similar, but the former is much smaller (as is the shell). Filopaludina gigantea has been considered as a large variety of F. bengalensis . The specimen of F. gigantea examined partly lacks the sandpaper-like layer and instead exhibits a smooth maroon nuclear region that, if confirmed as being present in more specimens, might be a size-independent character for distinguishing the two species.

The operculum of F. luzonica stands out because of the conspicuous difference in colour between the marginal and enamel regions. This character is absent in the other Filopaludina species examined but is present in other genera, such as Idiopoma and Taia ( Table 2 ).

Figures

Figure 4. Interior surface of opercula of the viviparid species studied. A. Celetaia persculpta. B. Ussuripaludina ussuriensis. C. Sinotaia angularis. D. Anularya mansuyi. E. Anularya bicostata. F. Torotaia mainitensis. G. Neothauma tanganyicense. H. Bellamya phthinotropis. I. Bellamya trochlearis. J. Idiopoma umbilicata. K. Idiopoma dissimilis. L. Filopaludina luzonica. M. Filopaludina martensi. N. Filopaludina bengalensis. O. Filopaludina gigantea. P. Trochotaia trochoides. ƍ. Taia naticoides. R. Taia shanensis. S. Notopala ampullaroides. T. Angulyagra cf. polyzonata. Scale bar: 5 mm.

Figure 5. Exterior surface of opercula of the viviparid species studied. A. Celetaia persculpta. B. Ussuripaludina ussuriensis. C. Sinotaia angularis. D. Anularya mansuyi. E. Anularya bicostata. F. Torotaia mainitensis. G. Neothauma tanganyicense. H. Bellamya phthinotropis. I. Bellamya trochlearis. J. Idiopoma umbilicata. K. Idiopoma dissimilis. L. Filopaludina luzonica. M. Filopaludina martensi. N. Filopaludina bengalensis. O. Filopaludina gigantea. P. Trochotaia trochoides. ƍ. Taia naticoides. R. Taia shanensis. S. Notopala ampullaroides. T. Angulyagra cf. polyzonata. Scale bar: 5 mm.

Figure 7. Shells of the viviparid species studied. A. Celetaia persculpta. B. Ussuripaludina ussuriensis. C. Sinotaia angularis. D. Anularya mansuyi. E. Anularya bicostata. F. Torotaia mainitensis. G. Neothauma tanganyicense. H. Bellamya phthinotropis. I. Bellamya trochlearis. J. Idiopoma umbilicata. K. Idiopoma dissimilis. L. Filopaludina luzonica. M. Filopaludina martensi. N. Filopaludina bengalensis. O. Filopaludina gigantea. P. Trochotaia trochoides. ƍ. Taia naticoides. R. Taia shanensis. S. Notopala ampullaroides. T. Angulyagra cf. polyzonata. Scale bar: 10 mm.