Populations of intertidal molluscs Littorina saxatilis from the White and the Barents Sea living under conditions of varying degrees of wave exposure were morphometrically investigated by populational samples and individual growth analyses. The molluscs from all the studied populations were characterized by an allometric shell growth, but the characteristics of the allometry were different in populations from places with a different degree of wave impact. The shell shape of L. saxatilis embryos (a starting point for allometric growth) differed neither between regions nor between populations with different wave action. However, an analysis of successive age cohorts demonstrated that a rapid growth in the first 2–3 years of life was accompanied by considerable allometric changes specific for strongly and moderately exposed shores. Consequently, the molluscs older than three years acquired a typical “exposed” or “moderate” shell morphotypes. Comparison of populational and individual growth data from the same populations revealed a similarity of the coefficients of variation. These observations support the hypothesis that the shell form differences in the populations under conditions of different wave action are established not by the ongoing selection of the specific “exposed” or “moderate” shell form but by the implementation of different specific allometric growth programs depending on the environment. Therefore, we propose that the wave action is not a “proximate” but the “ultimate” cause of the shell differences. The features of the allometric growth are already formed in different populations and apparently become a population-specific inherited allometric growth program.