The Chinese mystery snail, black snail, or trapdoor snail (Cipangopaludina chinensis), is a large freshwater snail with gills and an operculum, an aquatic gastropod mollusk in the family Viviparidae. The name "trapdoor snail" refers the operculum, an oval corneous plate that most snails in this clade possess. When the soft parts of the snail are fully retracted, the operculum seals the aperture of the shell, providing some protection against drying out and predation. Taxonomy Taxonomy of the introduced populations of Oriental mystery snails is confusing and there are many scientific names in use. There has also been debate regarding whether or not Cipangopaludina chinensis malleata and Cipangopaludina japonica in North America are synonymous and simply different phenotypes of the same species. For example USGS database considers the two as separate species. Smith (2000) argues that Cipangopaludina is a subgenus of Bellamya; however, because most North American literature does not use the genus Bellamya to refer to these introduced snails, Oriental mystery snails discussed here are referred to by the name Cipangopaludina. Literature cited in the USGS database regarding the Chinese mystery snail may employ the following names: Cipangopaludina chinensis, Cipangopaludina chinensis malleatus, Cipangopaludina chinensis malleata, Viviparus malleatus, Viviparus chinensis malleatus, Bellamya chinensis and Bellamya chinensis malleatus. Description Species of the genus Cipangopaludina can be identified by their relatively large globose shells and concentrically marked opercula. The shell is conical and thin but solid, with a sharp apex and relatively higher spire and distant body whorl. This species has a small and round umbilicus and the spire is produced at an angle of 65–80°. Cipangopaludina chinensis exhibits light coloration as a juvenile and olive green, greenish brown, brown or reddish brown pigmentation as an adult. The inner coloration is white to pale blue. The surface of the shell is smooth with clear growth lines. The shell has 6.0–7.0 whorls. Bellamya chinensis is a large gastropod species generally in shell height and in shell width, the largest being in height and wide. The shell height can reach up to . Cipangopaludina chinensis has a width to height ratio of 0.74–0.82. The aperture is ovoid with a simple outer lip and inner lip. In juveniles, the last shell whorl displays a distinct carina, and the shell contains grooves with 20 striae/mm between each groove. Juveniles also have a detailed pattern on their periostracum consisting of two apical and three body whorl rows of