Oncomelania is a genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of very small tropical freshwater snail
Freshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....

s, aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 gastropod mollusks in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

Pomatiopsidae is a family of small mainly freshwater snails with gills and an operculum, aquatic gastropod mollusks in the superfamily Rissooidea ....


These Oncomelania snails are distantly related to the marine periwinkle
Common Periwinkle
The common periwinkle or winkle, scientific name Littorina littorea, is a species of small edible sea snail, a marine gastropod mollusk which has gills and an operculum, and is classified within the family Littorinidae, the periwinkles....

, and more closely related to the small marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 snails of the family Rissoidae
Rissoidae is a large family of very small and minute sea snails with an operculum, marine gastropod mollusks in the clade Littorinimorpha.-Distribution and habitat:...



There are two species in the genus Oncomelania:
  • Oncomelania hupensis
    Oncomelania hupensis
    Oncomelania hupensis is a species of very small tropical freshwater snail, an aquatic gastropod mollusk in the family Pomatiopsidae.- Distribution :...

    Gredler, 1881 - type species, this polytypic
    In zoology, polytypic refers to a taxonomic unit with more than one subgroup at the next lower level.-See also:*Linnaean taxonomy*monotypic*monotypic habitat...

     species has a number of subspecies
  • Oncomelania minima
    Oncomelania minima
    Oncomelania minima is a species of freshwater snail, an aquatic gastropod mollusk in the family Pomatiopsidae.- Distribution :This species occurs in Ishikawa Prefecture and in Sado Island, Niigata Prefecture, Japan.It is Vulnerable species in Japan....

    P. Bartsch, 1936

Woodruff et al. (1999) recognized also the following species:
  • Oncomelania lindoensis Davis & Carney, 1973 - from Lake Lindu, Sulawesi
    Sulawesi is one of the four larger Sunda Islands of Indonesia and is situated between Borneo and the Maluku Islands. In Indonesia, only Sumatra, Borneo, and Papua are larger in territory, and only Java and Sumatra have larger Indonesian populations.- Etymology :The Portuguese were the first to...

Japanese Red List Data Book (2006) recognizes also the following additional species:
  • Oncomelania shini - as Vulnerable species
    Vulnerable species
    On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...

     in Japan
  • Oncomelania sakuyamai - with no conservation status evaluated in Japan


This genus has not yet become established in the USA, but it is considered to represent a potentially serious threat as a pest, an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

 which could negatively effect agriculture, natural ecosystems, human health or commerce. Therefore it has been suggested that this species be given top national quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....

 significance in the USA.


About the origin and evolution history of Oncomelania, Davis (1979) proposed a Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...

n origin for the Pomatiopsidae
Pomatiopsidae is a family of small mainly freshwater snails with gills and an operculum, aquatic gastropod mollusks in the superfamily Rissooidea ....

, with rafting to mainland Asia via the Indian Craton after break-up of Gondwanan and colonization of South-East Asia and China. It is hypothesized that Oncomelania snails, arrived in southwestern China from Indian before the second (major) Tibetan orogeny (2.5 Ma), then evolved and spread down their respective river systems, to mainland of China, Indonesia and Philippines. Although mutation rate calibrations using fossil data is impossible here, many studies have demonstrated the confidence that molecular data can provide reasonable estimates of divergence time. Data by Zhao et al. (2010) suggested that the two subspecies of Oncomelania hupensis
Oncomelania hupensis
Oncomelania hupensis is a species of very small tropical freshwater snail, an aquatic gastropod mollusk in the family Pomatiopsidae.- Distribution :...

began to diverse as early about 2–6 Ma based on the invertebrate ITS substitution rate range. Zhao et al. (2010) did not find any strong molecular and fossil evidences about Oncomelania evolution, but the reported Oncomelania fossil found in Guangxi
Guangxi, formerly romanized Kwangsi, is a province of southern China along its border with Vietnam. In 1958, it became the Guangxi Zhuang Autonomous Region of the People's Republic of China, a region with special privileges created specifically for the Zhuang people.Guangxi's location, in...

 (1 Ma) by Nils Hjalmar Odhner
Nils Hjalmar Odhner
Nils Hjalmar Odhner was a Swedish zoologist who studied mollusks, a malacologist. During his lifetime he was professor of invertebrate zoology at the Swedish Museum of Natural History, Stockholm...

 in 1930 and geological movement make this diversification time reasonable. It provides a new insight into the Oncomelania evolution history although the substitution rate needs to be verified with new fossil and molecular data in future study.


Various Oncomelania species are significant medically, because they can serve as vectors for two serious human diseases: they can carry the schistosomiasis
Schistosomiasis is a parasitic disease caused by several species of trematodes , a parasitic worm of the genus Schistosoma. Snails often act as an intermediary agent for the infectious diseases until a new human host is found...

 blood fluke parasite, and the paragonimus
Paragonimus is an important genus of flatworms, or platyhelminths, that includes Paragonimus westermani, an infectious lung fluke endemic to Asia....

 lung fluke parasites.

The miracidia reproduce asexually through sporocyst
Sporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...

 stages within these intermediate host
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...

s, resulting in the production of many free-swimming cercariae.
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