Invasion History

First Non-native North American Tidal Record: 2000
First Non-native West Coast Tidal Record: 2022
First Non-native East/Gulf Coast Tidal Record: 2000

General Invasion History:

The native and introduced ranges of Heterogen japonica are poorly known because of taxonomic confusion with Cipangopaludina chinensis. Heterogen japonica is native to Japan, Korea, and Taiwan, while a subspecies, C. c. maeta occurs in Japan (Clench and Fuller 1965; Jokinen 1982; Smith 2000; Hirano et al. 2015). Smith (2000) describes morphological features separating the two species and list records for shells matching the morphology of H. japonica. Records of this species appear to be more scattered than those of Cipangopaludina chinensis (Clench and Fuller 1965; Jokinen 1982; Smith 2000; Bury et al. 2007). It has however, been reported from 23 states (USGS Nonindigenous Aquatic Species Program 2022), but not from the western United States. Molecular studies (e.g., Fowler et al. 2022) may be needed to clarify the taxonomy and distribution of these large, conspicuous snails.

North American Invasion History:

Invasion History on the West Coast:

In 2022, Asian Mystery snails were sampled and genetically identified in the Hothouse Reservoir, in the middle Sacramento River basin, upstream of Sacramento,  All of the collected snails were identified as Hetrogen japonica (Abeyrathna et al. 2022). No specimens of Cipangopaludina chinensis were found in this reservoir Further genetic sampling will be needed to determine whether both species occur in the Delta (Abeyrathna et al. 2022),

Invasion History on the East Coast:

The earliest reported collection of Heterogen japonica on the East Coast to our knowledge is from Muddy River, Boston, Massachusetts in 1916 (MCZ Malacology 54908, Museum of Comparative Zoology 2013). Specimens of H. japonica have been identified from the Concord River, Massachusetts (Clench and Fuller 1965), a lake in the Hudson valley, New York (Jokinen 1992), and two lakes in the interior of Connecticut (Smith 2000). Heterogen japonica has been found, sometimes abundantly, in reservoirs in the interior of Virginia, North Carolina, and South Carolina (Dillon et al. 2006), and has been collected in ponds and reservoirs in Florida, Oklahoma, and Texas (Museum of Comparative Zoology 2013). Estuarine records are from the tidal fresh Connecticut River in Lyme, Connecticut (Smith 2000) and from the tidal Potomac River, in Arlington, Virginia in 2007 (Kraus 2007; USGS Nonindigenous Aquatic Species Program 2010). Previous records of Heterogen spp. from the Potomac have been identified as C. chinensis (Dundee 1974; US National Museum of Natural History collections). It is uncertain whether both species are present in the river. In recent years, shells resembling H. japonica (strongly conical) have been commonly seen floating or washed up on the shore of the Potomac River (Fofonoff, personal observations). Because of confusion between Heterogen japonica and Cipangopaludina chinensis, the dates of invasion of the two species are uncertain. Studies of shell collections and genetics of populations are desirable.

Heterogen japonica was reportedly introduced to Lake Erie in the 1940s as food for Channel Catfish (Ictalurus punctatus) by local fishermen (Wolfert and Hiltunen 1968). The extent of its range in the Great Lakes is uncertain, owing to confusion with C. chinensis (Mills et al. 1993).

Invasion History Elsewhere in the World:

Heterogen japonica is probably widely kept as an aquarium snail and released into urban waters, but is usually not distinguished from Cipangopaludina chinensis.


Heterogen japonica (Japanese Mystery Snail) is a large freshwater gastropod. The common name 'Mystery Snail' is applied to several snails of the family Viviparidae, which are kept in aquaria. Instead of laying egg masses, the snails brood their young. The release of the small, crawling snails can surprise aquarium-keepers,  The shell is dextrally coiled and somewhat globular, with a large aperture and sharply pointed spire. The umbilicus is small and partly covered by the parietal lip of the aperture. The aperture is large and oval. The operculum is brown with concentric growth lines. The shell is thin but strong. The adult shell has 6–7 whorls, which are strongly rounded and convex with clear sutures. The whorls are marked with transverse growth lines. The shell has a carina (keel) on the body whorl, which remains distinct as the shell grows. The spire forms a 50–55 degree angle. Shells may reach 60–75 mm in length. The color of the shell is light-brown to olive green, while the lip is black. Description from: Clench and Fuller 1965; Smith 2000; Jokinen 1992; Soes et al. 2011. 

The Japanese Mystery Snail has been frequently confused with the Chinese Mystery Snail (Cipangopaludina chinensis) which is roughly similar in shape and size. Both species co-occur in Japan and both species have been introduced to North America. Some authors have considered C. chinensis (Chinese Mystery Snail) and H. japonica to be conspecific, possibly ecophenotypes, while others have treated them as distinct (Clench and Fuller 1965; Jokinen 1982; Jokinen 1992). Smith (2000) provided a detailed morphological analysis, showing that the two forms show consistent differences, even as embryos in the brood pouch. Differences in the size of the larval shell (protoconch) contribute to differences in the shape of the adult shell, and the 'pointiness' of the spire, which is blunter in C. chinensis and sharper in H. japonica.  Smith (2000) applied the genus name Bellamya to the Chinese and Japanese 'mystery snails'. In a detailed morphological study of the Japanese Mystery SnailVan Bocxmaer and Strong (2016) restricted the genus Bellamya to African species, and reinstated the genus Cipangopaludina for the Asian snails. A molecular study of Japanese viviparids placed the Japanese snail in the genis Heterogen (Hirano et al. 2015).  Both species have been widely reported in North America, but the similarity of the two species make identifications uncertain. Ryan (2015) studied Mystery Snails in the Potomac River, and found many snails fitting the morphologies of both species with many intermediates in the Potomac River, and referred to the snails in the river as 'Bellamya spp.' Fowler et al. (2022) collected Mystery Snails in the tidal Potomac River, and found only H. japonica.




Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Prosobranchia
Order:   Architaenioglossa
Family:   Viviparidae
Genus:   Heterogen
Species:   japonica


Viviparus japonicus (von Martens, 1861)
Bellamya japonica (Smith, 2000)

Potentially Misidentified Species

Cipangopaludina chinensis
This Asian freshwater snail (Chinese Mystery Snail) is very similar, but has a less acute spire, more rounded whorls, and has a 'malleated' (with shallow dents) shell surface. The species are frequently confused, and once were regarded by some biologists as conspecific, so their range is uncertain (Smith 2000).

Viviparus georgianus
This North American freshwater snail (Banded Mystery Snail) is native to the Mississippi Basin and Southeast US. It is marked with four chestnut-colored bands (Clench and Fuller 1965; Jokinen 1992).



Heterogen japonica has not been reported from brackish habitats to our knowledge. It is generally found in lakes, ponds, or slow-flowing rivers with sandy to muddy substrates, often in densely vegetated areas (Clench and Fuller 1965; Jokinen 1982; Jokinen 1992). These snails prefer water with high levels of calcium ions, usually above 10 ppm, and at pH levels above 7.0 (Jokinen 1982; Jokinen 1992). However, in New York State, H. japonica was found at a pH of 6.3 (Jokinen 1992). Foods include bottom detritus and benthic microalgae. Some viviparids have the ability to filter-feed using the gills, but in C. chinensis, planktonic algae does not make up a significant part of the diet (Jokinen 1982; Solomon et al. 2010). These snails are prone to great population booms and busts. Large numbers of floating and washed-up dead shells of H. japonica were found in Sandusky Bay, and in 2007–2011 in the tidal Potomac River (Fofonoff, personal observations). Predators include crayfishes (Olden et al. 2009), catfishes (Wolfert and Hiltunen 1968), and probably air-breathing predators such as gulls, raccoons, otters, etc.


Algae, detrtus, phytoplankton


Catfish (Ameiurus, Ictalurus spp.,) Birds, Raccoon


Trophic Status:

Herbivore. suspension feeder


General HabitatNontidal FreshwaterNone
General HabitatTidal Fresh MarshNone
General HabitatCoarse Woody DebrisNone
General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatRockyNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Life History

Heterogen japonica (Japanese Mystery Snail) is a large, viviparous freshwater snail. It has separate sexes. Life history information is limited for H. japonica, but females tend to be larger than males (Wolfert and Hiltunen 1968). Its life history is presumed to be similar to that of Cipangopaludina chinensis , which can produce eggs in their first year, at about 40 mm, but most of the population's egg production took place in the 4th and 5th years (Stanczykowska et al. 1971). They can produce up to 102 embryos per brood (Crabbe 1929, cited by Jokinen 1982). Eggs are brooded in a uterus, and are hatched and released during the warmer months at about 5.5 mm shell length (Wolfert and Hiltunen 1968). A population in Sandusky Bay, Ohio, caught with 13 mm mesh, appeared to have two size classes, but animals smaller than 20 mm were not retained (Wolfert and Hiltunen 1968). These data suggest a longevity of at least 3 years.

Tolerances and Life History Parameters

Minimum Salinity (‰)0None
Broad Temperature RangeNoneCold Temeprate-Warm Temperate
Broad Salinity RangeNoneNontidal Limnetic-Tidal Limnetic

General Impacts

Heterogen japonica (Japanese Mystery Snail) is an attractive and popular aquarium and fishpond snail, as well as a food item once sold in Asian markets in the United States (Jokinen 1982). This snail is abundant in some regions and may have had local impacts on fisheries, either as food or by interfering with fishing. In Sandusky Bay, Lake Erie, 'fishermen often made seine hauls containing '2 tons' of snails' (Mills et al. 1993). However, it has been regarded as a relatively benign invader, with little known about its ecological impacts. Large die-offs of these snails have cluttered the shores of the tidal Potomac and South Carolina reservoirs producing unpleasant sights and odors (South Carolina Department of Natural Resources 2007; Fofonoff, personal observations). Experiments with C. chinensis in mesocosms suggest that Asian mystery snails can affect native snail populations, through competition (Solomon et al. 2010).

Regional Impacts

L096_CDA_L096 (Sandusky)Economic ImpactFisheries
Another early introduction of these snails into the Great Lakes occurred in Sandusky Bay, Lake Erie, Ohio, in the 1940s, when a bushel of Bellamya japonica (as Cipangopaludina japonica) was supposedly introduced to feed channel catfish (Wolfert and Hiltunen 1968). As they reached high densities in Sandusky Bay, fishermen often made seine hauls containing 2 tons of snails. The snails were regarded as a serious nuisance by fishermen (Wolfert and Hiltunen 1968).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
GL-I Lakes Huron, Superior and Michigan 1968 Def Estab
GL-II Lake Erie 1945 Def Estab
M040 Long Island Sound 2000 Def Estab
M130 Chesapeake Bay 2007 Def Estab
L043 _CDA_L043 (Door-Kewaunee) 1968 Def Estab
L096 _CDA_L096 (Sandusky) 1945 Def Estab
P090 San Francisco Bay 2022 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abeyrathna, Wijesooriya Arachchilage Nimanthi Upeksha; Sanders, Shawn H.; Barreto, Ashley; Davinack, (2023) First genetically confirmed report of the Japanese mystery snail, Heterogen japonica (Martens, 1861) from California more than a century after its first introduction, BioInvasions records 12: In press

Academy of Natural Sciences of Philadelphia 2002-2024a Malacology Collection Search. <missing URL>

Bury, Jennifer A.; Sietman, Bernard E.; Karns, Byron N. (2007) Distribution of the non-native viviparid snails, Bellamya chinensis and Viviparus georgianus, in Minnesota and the first record of Bellamya japonica from Wisconsin, Journal of Freshwater Ecology 22(4): 697-703

Clench, William J. (1962) A catalogue of the Viviparidae of North America with notes on the distribution of Viviparus georgianus Lea, Occasional Papers on Mollusks, Museum of Comparative Zoolgy, Harvard University 2(27): 261-287

Clench, William J.; Fuller, Samuel L. H (1965) The genus Viviparus in North America, Occasional Papers on Mollusks, Museum of Comparative Zoology, Harvard University 2(32): 385-412

David, Andrew A.; Cote, Sara C. (2019) Genetic evidence confirms the presence of the Japanese mystery snail, Cipangopaludina japonica (von Martens, 1861) (Caenogastropoda: Viviparidae) in northern New York, BioInvasions Records 8: 793-803

Dillon, R. T. Jr.; Watson, B.T.; Stewart, T. W.; Reeves, W. K. 2006-2024 The freshwater gastropods of North America.

Dundee, Dee S. (1974) Catalog of introduced molluscs of eastern North America (North of Mexico), Sterkiana 55: 1-37

Fowler, Amy E.; Loonam, Grace A.; Blakeslee, April M.H. (2022) Population structure and demography of non-indigenous Japanese mystery snails in freshwater habitats of Virginia and Washington, D.C., USA, Aquatic Invasions <missing volume>(Published onlin): Published online

Harvard Museum of Comparative Zoology 2008-2021 Museum of Comparative Zoology Collections database- Malacology Collection. <missing URL>

Hirano, Takahiro; Saito, Takumi; Chiba, Satoshi (2015) Phylogeny of freshwater viviparid snails in Japan, Journal of Molluscan Studies 81: 435-441

Johnson, Pieter T. J.; Olden, Julian D.; Solomon, Christopher T.; Vander Zanden, M. Jake (2009) Interactions among invaders: community and ecosystem effects of multiple invasive species in an experimental aquatic system, Oecologia 159: 161-170

Jokinen, Eileen H. (1982) Cipangopaludina chinensis (Gastropoda: Viviparidae) in North America, review and update, Nautilus 96(3): 89-95

Jokinen, Eileen H. (1992) The freshwater snails (Mollusca: Gastropoda) of New York State, New York State Museum Bulletin 482: 1-89

Kraus, Richard T. (2007) An Ecological Study of Gunston Cove, Fairfax County Department of Public Works, Fairfax County, VA. Pp. 148-158

Lehnert Helmut; Stone, Robert (2016) A comprehensive inventory of the Gulf of Alaska sponge fauna with the description of two new species and geographic range extensions, Zootaxa 4144: 365-382

Mills, Edward L.; Leach, Joseph H.; Carlton, James T.; Secor, Carol L. (1993) Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions., Journal of Great Lakes Research 19(1): 1-54

Örstan, Aydin 2007 Snail's Tales: Mysterious snails of the Potomac. <missing URL>

Perez, Bianca J.;Segrest, Averi Harp; Campos, Sofia R.; Minton, Russell L.; Burks, Romi L. (2016) First record of Japanese Mystery Snail Cipangopaludina japonica (von Martens, 1861) in Texas, Check List 12(1973): Published online

Ryan, Jeanne Michelle (2015) Histological and geospatial analysis of the mystery snail (Bellamya spp.) populations in the Potomac and Occoquan Rivers utilizing citizen scientist participation, George Mason University, <missing place>. Pp. <missing location>

Smith, Douglas G. (2000) Notes on the taxonomy of introduced Bellamya (Gastropoda: Viviparidae) species in northeastern North America., Nautilus 114(2): 31-37

Soes, D. Menno; Majoor, Gerard D.; Keulen, Stef M.A. (2011) Bellamya chinensis (Gray, 1834) (Gastropoda: Viviparidae), a new alien snail species for the European fauna, Aquatic Invasions 6: Corrected Proof

Solomon, Christopher T.; Olden, Julian D. Johnson, Pieter T. J.; Dillon Jr., Robert T.; Vander Zanden, M. Jake (2010) Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes, Biological Invasions 12: 1591-1605

South Carolina Department of Natural Resources (2007) <missing title>, South Carolina Department of Natural Resources, Columbia SC. Pp. 1-95

Stanczykowska, Anna, Magnin, Etienne, Dumouchel, André (1971) Etude de trois populations de Viviparus malleatus (Reeve) de la region de Montreal. 1. Croissance, fecondite, biomasse, et production annuelle., Canadian Journal of Zoology 49: 1431-1441

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

USGS Nonindigenous Aquatic Species Program 2003-2024 Nonindigenous Aquatic Species Database.

Wolfert; David R.; Hiltunen, Jarl K. (1968) Distribution and abundance of the Japanese snail, Viviparus japonicus, and associated macrobenthos in Sandusky Bay, Ohio, Ohio Journal of Science 68(1): 32-40