Fig. 7

The presence of the 60° misorientation peak in relative frequency versus misorientation angle diagrams for A. lessonii shells. The diagrams are deduced from EBSD scans; the positions of these are shown in inserts in (A) and (B). EBSD measurements are taken on different sections of the shell wall. The last two scans are taken on chamber walls that were secreted in Cd²⁺- and/or Pb²⁺-contaminated water (white star). Diagrams marked with a black star represent shell portions that formed in uncontaminated water. We observe in (A) and (B) the strong reduction of the 60° misorientation peak for shell portions that grew in contaminated environments, however, also a scatter in the degree of twin formation for those shell parts that formed in uncontaminated waters. We find a difference in 60° misorientation peak height for the species shown in (A) and in (B). For those shell sections that formed in unpolluted waters, twinned calcite is present. Those shell sections that formed in waters polluted with Cd²⁺ or Pb²⁺ contain significantly less or possibly no twinned calcite. (C) Box-whisker plot statistically showing the comparison between the 60° peak in shell areas grown in unpoisoned and poisoned areas. Poisoning appears to decrease the height of the peak for both elements.