Molluscan Shell Pigments: an in Situ Resonance Raman Study

Using Resonance Raman microspectrometry we identify polyenes as shell pigments in 13 gastropod, 1 cephalopod and 4 bivalve taxa. The pigments are either isolated polyenes or polyenes bound to other molecules. Polyenes are present in coloured parts of the shell of all investigated taxa. Pigments differ between taxa and there is no trivial relationship between colour, pigment and taxon. The same colour in different taxa may be due to different pigments; different colours in the same taxon are due to different pigments; different colour saturation is due to different concentration of the same pigment. The pigment polyenes are unsubstituted chains of 8–13 conjugated double-bonds (16–26 carbon atoms) in the chain, with terminals incorporating –CH3 groups. This is the first demonstration of polyenes as shell pigment in the Mollusca. We also identify a carotenoid as the external, yellow pigment in Cypraea moneta.