At MAM tomorrow I will give a short presentation about the smallest land snails, specifically the ones that live in North America. I discussed relevant subjects in 2 posts in the summer of 2005 here and here.
Here are 2 of the pictures I will be showing tomorrow.
One of the smallest land snails in North America is Punctum smithi; its largest adult shells are about 1.2 mm in diameter. The largest native land snail in eastern North America is Neohelix albolabris, the adult shell diameter of which can exceed 30 mm. The picture above shows the half of a N. albolabris shell. Inside it, I placed a P. smithi shell near the lower left corner.
As the shell of a snail gets smaller, its shell gets thinner. This is necessary, because otherwise there wouldn't be any room left inside the shell for the snail. In the picture below you can see that the P. smithi shell is about as high as the N. albolabris shell is thick.
The shells of the newly hatched P. smithi and other equally small species must be even thinner and fragile.