I have written about the little semi-terrestrial snail Pedipes ovalis in this post and this post. A small number of them that I collected in Florida in April 2009 and brought home to Maryland stayed alive for several months and provided me with hours of fun and enlightenment.
The shell aperture of Pedipes ovalis is surrounded by two columellar and one prominent parietal teeth.
A characteristic of the genus is the anatomy of the foot, which is divided by a transverse groove into an anterior propodium and a posterior metapodium.
A casual examination of a specimen preserved in alcohol led me to a hypothesis to explain the function of the long parietal tooth. A short paper detailing my ideas just came out in Basteria, the journal of the Netherlands Malacological Society*.
Unfortunately, Basteria won't let me post the paper on the Web for a year. But if you want a pdf copy, send me an e-mail and I'll happy to send you one.
Here is the abstract from the paper.
When Pedipes ovalis withdraws into its shell, its foot is sequestered between the parietal and the columellar teeth, while the sinus above the parietal tooth encloses the portion of the mantle skirt with the pneumostome. This organization suggests that one function of the long parietal tooth characteristic of the genus is to prevent the snail’s foot from blocking the pneumostome.
*Örstan, A. 2010. A possible function of the parietal tooth of Pedipes (Gastropoda, Pulmonata, Ellobiidae). Basteria 74:111-114.