Biomphalaria straminea is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails. This snail is a medically important pest, because an intermediate host for the parasite Schistosoma mansoni and a vector of schistosomiasis. The history of these discoveries was summarized by Paraense (2001). The shell of this species, like all planorbids is sinistral in coiling, but is carried upside down and thus appears to be dextral.