Abstract
Calcareous layers (ostracum) of mollusc shells are covered by thin organic layer (periostracum) which protects them against environmental influences. Land snails being perfectly adapted on various condition inhabit wide range of habitats.
Such adaptations comprise also microarchitecture of the shell wall. We compare closely related species (mainly members of families Vertiginidae and Valloniidae), which differ in their ecological requirements.
Periostracum of species living in wet and acid habitats (e.g. genus Columella, some members of genus Vertigo and Acanthinula aculeata) is usually two-layered and thicker than that of calciphilous or mesic species. In extreme cases (e.g.
Columella aspera and Zoogenetes harpa), periostracum reaches one third of total shell thickness and possess multi-layered structure. On the other hand, species living in dry and/or calcium rich environment have one-layered and relatively thin periostracum.
The periostracum of some Vallonia species and Vertigo pygmaea reaches only two or three percent of total shell wall thickness. Still, microstructural shell characters together with inner structure of the periostracum remain understudied and represent unknown land snail adaptation for various habitat condition.