I spent my first afternoon in Florida yesterday collecting Cerithidea scalariformis a "marine" snail that spends its adult live on land. The snails I found were all on damp sand under mangroves as much as about 10 meters away from the sea. According to Houbrick (American Malacological Bulletin, 2: 1-20, 1984), C. scalariformis deposits its eggs in the sea. As the snails grow, they leave the sea and gradually move away from it. They seem to stay always within reach of the tides, but when the tide comes in, the adults climb on plants to avoid getting immersed.
Houbrick also noted that the shells of female snails were slightly larger than those of males. The reproduction of Houbrick's work would require dissection of a large number of snails to sex them, which is something I don't intend to do. Instead, I thought if I measured a large number of snails, I could perhaps tell from histograms of measurements if there were 2 groups. So I spent several hours last nite measuring Cerithidea.
I will measure another batch this morning before I return the snails to where I got them from. The nice thing about working with C. scalariformis is that they don't seem to mind being dry for many hours and after they are put back on damp sand in a plastic container, they resume their activities.