Taking advantage of the last days of the summer, my son and I went on a nature hike in the woods yesterday afternoon. While passing by some small, shallow pools alongside the creek, I noticed these tracks on the submerged rocks. I suspected snails and sure enough, a couple of the tracks each ended at a small roundish object that indeed was a snail about 5 mm long.
I am guessing that they are juvenile Helisoma anceps, a planorbid snail (family Planorbidae). Although they are strictly aquatic, these snails actually have lungs and are in the subclass Pulmonata along with many strictly terrestrial snails. The planorbid snails have evolved an accessory gill, the pseudobranch, that helps them extract oxygen from the water.
We may return to the creek later this afternoon to collect some of these snails with the purpose of raising them at home for a while. I am hoping to take photographs of the snails themselves.