For aquatic gastropods the anterior positioning may be useful for preventing sediment getting into the mantle cavity, which is more likely with a posterior positioning due to sediment being stirred up by the motion of the gastropod.
The anterior positioning may be useful for preventing sediment. This is for aquatic gastropods. This sediment is getting into the mantle cavity. The mantle cavity is more likely with a posterior positioning due to sediment being stirred up by the motion of the gastropod.