Formation of clausiliar apparatus in Vestia gulo (E. A. Bielz) was analysed and illustrated with SEM photographs. The sequence of formation of apertural barriers is the following: 1) inferior and spiral lamellae, 2) superior lamella, subcolumellar lamella, clausilium, principal palatal plica, 3) lunella and other palatal folds. Under laboratory conditions the closing apparatus developed during two weeks. The shell development in V. gulo was compared with literature data on another clausiliid, Herilla bosniensis. Adaptive significanceof the rapid development ofapertural barriers is discussed in relation to the reproductive biology of Clausiliidae.