Mollusks, particularly gastropods, are excellent indicators of their environmental conditions. When studied in conjunction with other organisms, they can provide valuable insights into paleoenvironmental conditions. They occur in fossil record from the Cambrian to the Quartenary, in rocks formed in marine, freshwater and terrestrial conditions. To illustrate the information that freshwater and terrestrial gastropods can provide, we will examine several examples from the Tertiary period in Bohemia, where their lives were affected by volcanism.