Biomphalaria is a genus of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram’s horn snails.

This genus of snails is medically important because the snails can carry a parasite which represents a serious disease risk to humans; the snails serve as an intermediate host (vector) for the human parasitic blood fluke, Schistosoma mansoni.

The fluke, which is found primarily in tropical areas, infects mammals (including humans) via contact with water that contains schistosome larvae (cercariae) which have previously been released from the snail. Infection occurs via penetration of cercariae through the skin. In humans this fluke causes the debilitating disease schistosomiasis.

Other flukes which parasitize snails include Schistosoma japonicum, which parasitizes snails in the genus Oncomelania, and Schistosoma mekongi, which parasitizes snails in the genus Tricula.