The examples of pulmonate snails with extra space in their shells that I had in my two previous posts on this subject (#1 and #2) were all relatively large. What about smaller snails? Do they also carry extra space in their shells?
This photograph shows a live Euconulus polygyratus. Its shell is 2.3 mm long and 2.8 mm wide. We found this snail a couple of weekends ago during our field trip in Cunningham Falls State Park. A few days after I brought it to the lab, I noticed that the snail had become dormant on the underside of the lid of its container. As the photograph shows, the snail’s body (arrow) was about a third of a whorl behind the aperture.
So, yes, even small snails carry extra space in their shells.