THE ASSOCIATION BETWEEN MICROSTRUCTURE AND DISSOLUTION PATTERNS OBSERVED THROUGH SCANNING ELECTRON MICROSCOPY OF EXTANT EPITONIUM TINCTUM

Scanning electron microscopy imaging of extant Epitonium tinctum shells collected from the Gulf of Mexico shows a possible link between microstructure and dissolution patterns. These mesogastropods are high-spired with well-rounded whorls and sharp varicies that represent previous positions of the outer lip. Varicies and intervarical areas differ in microstructure, and cathodoluminescence studies suggest that their chemical composition may also vary. These microstructural and compositional differences lead to differences in dissolution patterns. Intervarical areas have spherulitic microstructure and initial dissolution appears as regularly spaced, circular pores. These pores are closely associated with features interpreted as representing advanced dissolution. These irregular features appear more frequently near the top of the shells, which supports the hypothesis that these features represent advanced dissolution, as dissolution should be more frequent and advanced in older parts of the shells. The pattern of regular dissolution suggests that the spherulitic microstructure of the interareas controls initial dissolution. In contrast, dissolution of the ribs does not have a regular pattern.

SEM imaging of the shells suggests that the varicies are more resistant to dissolution; in contrast, dissolution of the intervarical areas begins while these snails are alive. Therefore, pristine shell material needed for geochemical studies may be more readily obtained from the varicies, although they form episodically during growth. Recognition of the association between microstructure and dissolution also allows for preliminary recognition of microstructural differences between species, or even within different shell parts, prior to microanalytic analyses.