On morphology, function and taxonomic importance of the shell ribs in Clausiliidae (Mollusca: Gastropoda Pulmonata), with special reference to those in Albinaria

In Clausiliidae, Urocoptidae and a few other groups the shell ribs are not solid, but hollow and provided with complicated structures inside. These structures are described and illustrated. Their presence may be correlated with a certain habitat, at least within a polymorphic species. Several physical consequences of ribs are suggested and some are experimentally tested. Especially shell weight and strength, surface water adhesion, shell permeability and warming up after insolation are dealt with. The possible adaptive value is discussed.