taxonID	type	description	language	source
74498794FF83E41AFC302F17FC73020F.taxon	materials_examined	Examined species: Amuropaludina praerosa (Gerstfeldt, 1859)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFC302F17FC73020F.taxon	description	(Figs 2 H, 3 H, 6 H).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFC302F17FC73020F.taxon	discussion	Remarks: Within Viviparidae, Amuropaludina is the only genus with an operculum that has a central nucleus. All other genera of Viviparidae have an operculum with a subcentral nucleus. The wide semi-elliptical shape of Amuropaludina is also a useful diagnostic character.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFEC32F9EFEC90284.taxon	materials_examined	Examined species: Campeloma decisum (Say, 1817)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFEC32F9EFEC90284.taxon	description	(Figs 2 B, 3 B, 6 B).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFEC32F9EFEC90284.taxon	discussion	Remarks: The elongated, inverted-comma-shaped and concentric operculum is the most important combination of diagnostic opercular characters for Campeloma. The apex – nucleus distance is clearly longer than the base – nucleus distance. This character is seen only in Campeloma and Lioplax, the two extant genera of Lioplacinae.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFBF82DB9FA4700B3.taxon	materials_examined	Examined species: Lioplax subcarinata (Say, 1817) (Figs 2 A, 3 A, 6 A).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41AFBF82DB9FA4700B3.taxon	discussion	Remarks: Lioplax is the only genus in the family with a paucispiral operculum at early developmental stages, which is different from the concentric operculum of all other genera of Viviparidae. In addition, the semi-elliptical shape and lower central location of the nucleus are also diagnostic opercular characters for this genus.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41BFBFD2E33FEDD0232.taxon	materials_examined	Examined species: Callinina georgiana (Lea, 1834) (Figs 2 C, D, 3 C, D, 6 C, D); C. intertexta (Say, 1829) (Figs 2 E, 3 E, 6 E).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF83E41BFBFD2E33FEDD0232.taxon	discussion	Remarks: Callinina can be distinguished from Viviparus and the other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a thin marginal region that obviously differs in colour from the enamel region; a shiny, smooth and relatively small nuclear region; and a narrow inner enamel region. The only opercular difference found between the two examined species was a relatively darker and thicker operculum in the single examined individual of C. intertexta as compared with C. georgiana.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF82E41BFEAA2E40FC570393.taxon	description	(Figs 2 G, 3 G, 6 G).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF82E41BFEAA2E40FC570393.taxon	discussion	Remarks: The semi-elliptical operculum of Rivularia is most similar to that of Tulotoma. However, the operculum of Rivularia has no obvious marginal region; there is, however, a smooth, large scar region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF82E418FC012FAFFF31035E.taxon	materials_examined	Examined species: Tulotoma magnifica (Conrad, 1834) (Figs 2 F, 3 F, 6 F).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF82E418FC012FAFFF31035E.taxon	discussion	Remarks: The operculum of Tulotoma can be easily distinguished from that of all other genera based on the following characters: semi-elliptical shape; inwardly folded opercular apex and opercular base; outwardly folded inner margin; a rough, nontransparent and small inner opercular region; and a wide, thin marginal region that obviously differs in colour from the enamel region, especially when it is compared with Rivularia Heude, 1890. Like Tulotoma, Rivularia has a semi-elliptical shape and subcentral nucleus.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF81E418FEBD2F64FA5C0333.taxon	materials_examined	Examined species: Viviparus viviparus (Linnaeus, 1758) (Figs 2 I, 3 I, 6 I); V. contectus Millet, 1813 (Figs 2 J, K, 3 J, K, 6 J, K).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF81E418FEBD2F64FA5C0333.taxon	discussion	Remarks: Viviparus can be distinguished from the other genera with a concentric inverted-comma-shaped operculum (especially Callinina) by the following combination of characters: a thickened marginal region, obvious concentric growth grooves on the interior surface, a wide inner enamel region, and a small and smooth nuclear region. The operculum of V. contectus differs from that of V. viviparus in having a thicker marginal region and more obvious grooves.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF81E419FBFC2F79FDBF0315.taxon	materials_examined	Examined species: Angulyagra cf. polyzonata (Frauenfeld, 1862)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF81E419FBFC2F79FDBF0315.taxon	description	(Figs 4 T, 5 T, 7 T).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF81E419FBFC2F79FDBF0315.taxon	discussion	Remarks: Apart from Notopala, Angulyagra can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a relatively small nuclear region with shiny grains or veins, a relatively thick enamel layer and a thin marginal region that obviously differs in colour from the enamel region. One species of Angulyagra (total of three specimens with operculum) has been examined for this study (Table 1).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FEC12F29FBE30315.taxon	materials_examined	Examined species: Anularya mansuyi (Dautzenberg & Fischer, 1905)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FEC12F29FBE30315.taxon	description	(Figs 4 D, 5 D, 7 D);	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FEC12F29FBE30315.taxon	discussion	Remarks: Except for the larger overall size and inner opercular region, the operculum of Anularya is most similar to that of Sinotaia. Apart from Sinotaia, Anularya can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a thick, smooth, shiny, nontransparent and small nuclear region and a thick enamel region. The operculum of A. mansuyi differs from that of A. bicostata by having a more acute opercular apex. The thickness of the adult operculum of A. mansuyi can vary from relatively thin to thick. Therefore, its colour can be transparent orange red to relatively nontransparent dark red.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FC1A2F29FC6D0284.taxon	materials_examined	Examined species: Bellamya phthinotropis (Martens, 1892)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FC1A2F29FC6D0284.taxon	description	(Figs 4 H, 5 H, 7 H);	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF80E419FC1A2F29FC6D0284.taxon	discussion	Remarks: Bellamya can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: opercular height almost as same as width; a small, smooth shiny nuclear region; and a thin and narrow marginal region. The operculum of B. trochlearis differs from that of the other species examined, B. phthinotropis, by having a more notably convex outer margin — this fits the shape of the aperture and has a strong keel.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FE902CC3FD9203D3.taxon	materials_examined	Examined species: Celetaia persculpta (Sarasin & Sarasin, 1898)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FE902CC3FD9203D3.taxon	description	(Figs 4 A, 5 A, 7 A).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FE902CC3FD9203D3.taxon	discussion	Remarks: Apart from Torotaia, Celetaia can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a blunt opercular apex; a large, smooth and shiny nuclear region, sometimes surrounded by concentric veins; and a thin marginal region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FC582F4FFC0103E4.taxon	description	(Figs 2 Q, 3 Q, 6 Q)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FC582F4FFC0103E4.taxon	discussion	Remarks: This species has a large nuclear region with a sandpaper-like layer (nontransparent); this layer is sometimes partly or even completely absent in the nuclear region of some individuals, especially juveniles.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FED02FEFFA1B0330.taxon	materials_examined	Examined species: Cipangopaludina chinensis (Gray, 1834);	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE416FED02FEFFA1B0330.taxon	discussion	Remarks: The Cipangopaludina species examined have a similar operculum, which can be distinguished from the other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: regular growth lamellae on the exterior surface, a relatively small inner operculum region and a large nuclear region with a sandpaper-like layer (sometimes partly absent).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE417FC692E1AFE7B0259.taxon	description	(Figs 2 O, 3 O, 6 O)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8FE417FC692E1AFE7B0259.taxon	discussion	Remarks: Vivipara nagaensis Preston, 1914 has been rarely mentioned in the literature after its description. Here, it is classified as a species of Cipangopaludina based on its shell morphology and the fact that it exhibits the generic characters of the Cipangopaludina operculum (i. e. as seen in the type species of the genus, C. chinensis). The shell and operculum of C. nagaensis are much smaller than those in C. chinensis and only a small part of the nuclear region in C. nagaensis is covered by the sandpaper-like layer.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8EE414FF4F2E65FEB10203.taxon	description	(Figs 2 P, 3 P, 6 P)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8EE414FF4F2E65FEB10203.taxon	discussion	Remarks: Vivipara crassibuca Sarasin & Sarasin, 1898 has been rarely mentioned after its description. Prashad (1928) regarded it as undoubtedly belonging to Cipangopaludina based on shell morphology. Schuh et al. (2010) assigned this species to Idiopoma in their online database but provided no justification. Here, we assign it to Cipangopaludina based on its shell morphology and the fact that its operculum exhibits the generic characters of Cipangopaludina. The operculum of C. crassibuca has denser growth lamellae compared to the other two species of Cipangopaludina examined. In addition, the convex inner margin of the first species is not as pronounced as in the other two species.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8DE415FEA02E3FFF2F0749.taxon	materials_examined	Examined species: Filopaludina martensi (Frauenfeld, 1864)	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8DE415FEA02E3FFF2F0749.taxon	description	(Figs 4 M, 5 M, 7 M); Filopaludina bengalensis (Lamarck, 1822) (Figs 4 N, 5 N, 7 N); Filopaludina gigantea (von dem Busch, 1843) (Figs 4 O, 5 O, 7 O); Filopaludina luzonica (Kobelt, 1909) (Figs 4 L, 5 L, 7 L).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8DE415FEA02E3FFF2F0749.taxon	discussion	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).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FEB12B75FE6A017F.taxon	materials_examined	Examined species: Heterogen longispira (E. A. Smith, 1886) (Figs 2 S, 3 S, 6 S); Heterogen japonica (Martens, 1861) (Figs 2 T, 3 T, 6 T).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FEB12B75FE6A017F.taxon	discussion	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., 2019 a); 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.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FEA62D83FE5E0333.taxon	materials_examined	Examined species: Idiopoma umbilicata (Lea, 1856) (Figs 4 J, 5 J, 7 J); Idiopoma dissimilis (Müller, 1774) (Figs 4 K, 5 K, 7 K).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FEA62D83FE5E0333.taxon	discussion	Remarks: Idiopoma can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a whole inner opercular region covered by a thick, rough, brownish-yellow sandpaper-like layer; a thin marginal region obviously differing from the enamel region in colour; and an enamel region that is smooth but has a fine grid-like pattern. The operculum of I. dissimilis is about as high as it is wide, while in I. umbilicata the operculum is distinctly higher than it is wide. This difference can be attributed to differences in aperture shape between the two species.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FE912F4EFD950229.taxon	materials_examined	Examined species: Margarya melanioides (Dautzenberg & Fischer, 1905) (Figs 2 R, 3 R, 6 R).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FE912F4EFD950229.taxon	discussion	Remarks: Margarya can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a large nuclear region with many grains and veins, and a large inner opercular region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FEE32E55FC310464.taxon	materials_examined	Examined species: Mekongia jullieni (Deshayes, 1876) (Figs 2 L, 3 L, 6 L). Remarks: Mekongia is not a monophyletic group according to two recent molecular systematic studies (Hirano et al., 2019 a; 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.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FC10289AFA8707B8.taxon	materials_examined	Examined species: Neothauma tanganyicense E. A. Smith, 1880 (Figs 4 G, 5 G, 7 G).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FC10289AFA8707B8.taxon	discussion	Remarks: Apart from Mekongia, the monotypic genus Neothauma can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: height clearly larger than width and a small nuclear region that is relatively rough, with many shiny grains or veins.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBF82BC6FBF406DC.taxon	materials_examined	Examined species: Notopala ampullaroides (Reeve, 1863) (Figs 4 S, 5 S, 7 S).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBF82BC6FBF406DC.taxon	discussion	Remarks: Apart from Angulyagra, Notopala can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a relatively small nuclear region with shiny grains or veins, a relatively thick enamel layer and a thin marginal region that obviously differs in colour from the enamel region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBE62AE2FC5701CA.taxon	materials_examined	Examined species: Sinotaia angularis (Müller, 1774) (Figs 4 C, 5 C, 7 C).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBE62AE2FC5701CA.taxon	discussion	Remarks: Apart from Anularya, Sinotaia can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a thick, smooth, shiny, non-transparent and small nuclear region and a thick enamel region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBFF2DE8FC4703B4.taxon	materials_examined	Examined species: Taia naticoides (Kobelt, 1909) (Figs 4 Q, 5 Q, 7 Q); Taia shanensis (Kobelt, 1909) (Figs 4 R, 5 R, 7 R).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE415FBFF2DE8FC4703B4.taxon	discussion	Remarks: Taia can be distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a subcentral nucleus that is very close to the inner margin; a large nuclear region with many fine, dense grains or veins; an inner opercular region completely or partly covered by a rough sandpaper-like layer; an enamel region that is thickened and deeper in colour near the inner opercular region; and a thin, wide marginal region that obviously differs in colour from the enamel region. The inner nuclear region of T. shanensis is almost completely covered by a thick sandpaper-like layer, which is mostly absent in T. naticoides.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE412FC022FCAFEF00719.taxon	materials_examined	Examined species: Tchangmargarya yangtsunghaiensis (Tchang & Tsi, 1949) (Figs 2 N, 3 N, 6 M); Tchangmargarya multilabiata (Zhang & Chen, 2015) (Figs 2 M, 3 M, 6 N).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8CE412FC022FCAFEF00719.taxon	discussion	Remarks: The two species of Tchangmargarya examined show the largest opercular differences within one genus of Viviparidae. This is especially true of the position of the nucleus. Nevertheless, these two species can still be assigned to a single genus and distinguished from other genera with a concentric inverted-comma-shaped operculum by the following combination of characters: a nuclear region with many grains or veins, an enamel region that is thickened near the inner opercular region and deeper in colour, and a thin marginal region obviously differing in colour from the enamel region. The operculum of T. multilabiata is obviously different from that of T. yangtsunghaiensis. In the former, the nucleus is positioned close to the inner margin and inner opercular region is larger; while the outer inner and upper inner margins of T. yangtsunghaiensis are inwardly curved, in T. multilabiata only the upper inner margin is inwardly curved.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FE982B25FDD3063C.taxon	materials_examined	Examined species: Torotaia mainitensis (Bartsch, 1907) (Figs 4 F, 5 F, 7 F).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FE982B25FDD3063C.taxon	discussion	Remarks: The operculum of Torotaia is distinct from that of most genera, but similar to that of Celetaia in the following characters: a large, smooth and shiny nuclear region, which is sometimes surrounded by concentric veins, and a thin marginal region. However, the operculum of Torotaia is more fragile and thinner, with the apex being noticeably more acute than in Celetaia.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FEA32A41FEA90151.taxon	materials_examined	Examined species: Trochotaia trochoides (Martens, 1860) (Figs 4 P, 5 P, 7 P).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FEA32A41FEA90151.taxon	discussion	Remarks: Trochotaia can be distinguished from the other genera by a concentric inverted-comma-shaped operculum that exhibits the following combination of characters: a thick, rough layer with many grains or veins over the whole of the inner opercular region; a clearly convex outer margin; and a smooth enamel region with a dense ray-like pattern.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FF1D2D6DFCC90075.taxon	materials_examined	Examined species: Ussuripaludina ussuriensis (Gerstfeldt, 1859) (Figs 4 B, 5 B, 7 B).	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
74498794FF8BE412FF1D2D6DFCC90075.taxon	discussion	Remarks: Ussuripaludina can be distinguished from the other viviparid genera studied by a concentric inverted-comma-shaped operculum that shows the following combination of characters: a shiny, smooth and convex nuclear region; a shiny and smooth scar region; a relatively large inner opercular region; and a narrow marginal region.	en	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): 1-14, DOI: 10.1093/mollus/eyab008, URL: https://doi.org/10.1093/mollus/eyab008
