Fig. 3

Shell microstructure of A. lessonii specimens that lived first in natural environments ((A), (C)) and, for the secretion of the last few chambers, lived in water contaminated with either Cd²⁺ or Pb²⁺ ((B), (D)). (A) to (D): EBSD scans showing crystal orientation. Yellow rectangles in inserts in (B), (D) indicate the position of EBSD scans shown in (B) and (D). In those shells where calcite growth takes place entirely in natural environments, the morphology of crystals within the at last formed chambers is euhedral and crystal sizes are in the very few micrometer range (this study and Fig. 11 in Yin et al. (2021)⁶). This is also the case at last secreted chamber walls of species that were secreted in polluted environments ((B), (D)). There is no marked difference in microstructure, crystal size or crystal morphology between shell sections secreted under natural and under poisoned conditions.