The Chinese mystery snail, black snail, or trapdoor snail (Margarya 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 40 millimetres (1.6 in) in shell height and 30 millimetres (1.2 in) in shell width, the largest being 60 millimetres (2.4 in) in height and 40 millimetres (1.6 in) wide. The shell height can reach up to 65 millimetres (2.6 in). 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 hairs with long hooks on the ends, distinct ridges and many other hairs with short hooks. The shell of Cipangopaludina chinensis grows allometrically (the height increasing faster than the width) and does so at a decreased rate in comparison with Cipangopaludina japonica, such that the adult shell is less elongate than that of its congener. The radula also may differ between Cipangopaludina japonica and Cipangopaludina chinensis, but there is so much variation even within one species that it is not a good diagnostic characteristic. However, as a general guide, in one North American population, the radula of Cipangopaludina chinensis had seven small cusps on the marginal tooth and a large central cusp with four small cusps on either side. Mystery snails (unlike apple snails) do not possess a siphon. They give live birth, and like all aquatic snails they only have one set of tentacles.
Distribution Though native to East Asia from the tropics of Indochina to northern China, this species has established itself in North America. The native range is from Southeast Asia to East Asia. This species is widely distributed in China including the Chinese Loess Plateau.
Nonindigenous distribution
United States This species was sold in Chinese food markets in San Francisco in the late 1800s. It was collected as early as 1914 in Boston. It was probably released from an aquarium into the Niagara River between 1931 and 1942. It has become a problematic invasive species in many areas. This snail is an introduced species in the United States. It is found in "any or all of the tributaries on Grand Island and on both sides of the Niagara River in the United States and Canada." The nonindigenous distribution in the USA include:
various ponds in Connecticut and Massachusetts; various ponds in New Hampshire; Potomac River, Maryland; Cocheco River, New Hampshire; Delaware River, New Jersey; Hudson River and Niagara River, New York; Schuylkill River and Susquehanna River, Pennsylvania; Annaquatucket River, Rhode Island; Lake Butte des Morts, Wisconsin a few isolated locations in Maine and Virginia. Minnesota: 80 waters known as of 2016 Great Lakes Region: The first record of Cipangopaludina chinensis malleata in the Great Lakes dates from some time between 1931 and 1942 from the Niagara River, which flows into Lake Ontario. Cipangopaludina chinensis malleata occurs in Lake Erie, where it was introduced some time prior to 1968. Cipangopaludina chinensis was found for the first time in Oneida Lake, which flows to Lake Ontario, in 1977–1978. Jokinen (1982) records occurrences of populations of Cipangopaludina chinensis in the drainages of Lake Erie, Lake Ontario and Lake Michigan, from the states of Michigan, Indiana, Ohio, Wisconsin, and New York. It was first reported from Lake Champlain in 2003. It is regulated in Minnesota where it is illegal to release it into the wild.
United Kingdom The Chinese mystery snail was first recorded in England from a ditch in the Pevensey Levels in Sussex in September 2018 and early in 2022 a second population was reported on iNaturalist from Southampton Common. This was investigated by Natural England and the snails were found to be present in a boating lake and an ornamental lake on the Common. How the snails were introduced is unknown but it was either through release from aquaria or from snails imported for food.
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