The distribution of polyenes in the shell of Arctica islandica from North Atlantic localities: a confocal Raman microscopy study

Many of the pigments that are widely found in coloured parts of mollusc shells are polyenes, i.e. molecules\udwith a central polyenic chain (carbon-carbon single and double bonds). Due to a resonant coupling\udof these molecules at wavelengths typically used in Raman spectroscopy, this method is well suited\udto investigate their occurrence in biogenic materials. Here we use confocal Raman microscopy to map\udthe spatial distribution of polyenes within the shell of the bivalve Arctica islandica and to determine their\udchemical characteristics (chain length). Polyene chain length does not differ between shells from different\udlocalities (off Iceland, Baltic Sea and North Sea). We also show that the pigment polyenes are not\udonly located at the outside of the shell, but also within the shell, developing the same layered pattern\udtypical for growth bands. This finding raises the question as to whether polyenes may play a role in the\udbiomineralization process itself