Planorbis stramineus 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,[1] because an intermediate host for the parasite Schistosoma mansoni and a vector of schistosomiasis.

[3] The shell of this species, like all planorbids is sinistral in coiling, but is carried upside down and thus appears to be dextral.

Schistosoma mansoni came to Neotropics from Africa in context of the slave trade.

[8] Schistosoma mansoni was not able to infect Biomphalaria straminea previously and it has adapted to this host.