Farbmusterumschlag auf der Molluskenschale

Summary

The variability of the shell pattern ofTheodoxus (Werrapopulation) is reduced to three significant types, which are based on different processes of pigment formation of the mantle-edge. A change between the ‘synchronen Querstreifen’-pattern and the ‘phasenlängenkonstanten Längsstreifen’-pattern is described. This change can be achieved at any time on the growing shell by altering the ionic composition of the external medium, i.e. these two types of pattern are determined stage by stage in the successive parts of the shell.