Stereo microscopic (A) and SEM (B,C) images of shell sections with organic covered spots on otherwise dissolved nacreous surfaces.

<p>(A) cross section through a shell piece with corroded nacre surface (white) and organic covered spots (blue), see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024223#pone-0024223-g003" target="_blank">Fig. 3</a> for larger SEM magnification of the upper part of the shell cross section. (B) SEM image of the same shell piece displayed in (A), illustrating nacreous and prismatic layers, as well as an amorphous structure on the location of the blue spot (S) which presumably is transparent and organic, as the characteristic light refraction pattern of the underlying nacreous layer is conserved in ‘spot’ areas, see (A). (C) SEM image from strongly corroded shell area, with blue spot elevated several µm above the surface. This shell region also appears to be covered with protective organic material.