Most land snail species that have teeth or lamellae in the
apertures of their shells develop them as they near sexual
maturity. In a handful of species, such apertural formations are
present in young snails, but diminish in number and size or
disappear completely in adults. The North American snail
Ventridens suppressus is in the latter group. The apertures of
the shells of newly hatched Ventridens suppressus are
unobstructed. Up to 5 lamellae develop in their apertures as the
snails go thru their ontogeny. But as they approach maturity,
the lamellae get resorbed one by one and the adults end up with
1 small tooth. Sometimes even that disappears completely. Here
is one individual that I found recently (shell diameter was ~5
mm). It has 2 lamellae in its aperture. This is Pilsbry's 3rd
neanic substage (Fig. 235 in Land Mollusca of North America,
vol. II:1). In a paper that came out about a year ago, I
hypothesized that in the aperture of the shell of the semi-
terrestrial snail Pedipes ovalis, one long lamellae