Oncomelania hupensis is a species of very small tropical freshwater snail, an aquatic gastropod mollusk in the family Pomatiopsidae.
Over the past a few decades, the taxonomy of Oncomelania hupensis has been a dispute due to the variation in morphological characters such as shell sculpture, operculum etc. Phenotypically, Oncomelania hupensis can be separated into ribbed- and smooth- shelled morphotypes. In China, the typical morphotype of Oncomelania hupensis is ribbed-shelled, and its distribution is restricted to Yangtze River basin. Smooth-shelled snails are also distributed in mainland China, but are considered the same species and subspecies of Oncomelania hupensis.
Oncomelania hupensis reported in other Far East countries are smooth-shelled, and have been considered either as subspecies of Oncomelania hupensis or independent species in this genus.
Oncomelania hupensis has been found in China, Taiwan, and also in Japan, the Philippines, and on the Indonesian island of Sulawesi.
It is seasonally amphibious species which lives in lakes and on marshy ground.
The habitats of Oncomelania hupensis in the middle and lower reaches of the Yangtze River include lake/marshland regions and hill regions, both of which have extensive physical connections with the Yangtze River through channels or in low floodplains beside the Yangtze River. With frequent floodings of the Yangtze River, snails in these habitats can be dispersed and subsequently deposited widely in various localities. The accumulation of mixed sources of snails can then generate genetically diversified populations of snails, leading to the existence of various haplotypes.
In Sichuan and Yunnan provinces in the upper reaches of the Yangtze River, Oncomelania hupensis robertsoni are distributed in mountainous areas, and are not subjected to flood influence as much as in the middle and lower reaches of the river. It is interesting to see that a relatively lower number of haplotypes were found in this region as compared with Oncomelania hupensis hupensis. It appears likely that there has been certain degree of isolation for these mountainous populations.
