Molluscan shells show great diversity in colour, which is due to many different classes of chemical compounds. The identification of the pigments found in the molluscan shells of a diverse group of marine species was done in situ using Resonance Raman spectroscopy, and found to be unsubstituted polyacetylenes. Two South African species (D. serra and J. janthina) were chosen for extraction of the pigment-containing organic component, and it was found that the vibrational bands in the Raman spectra of the extracted component shifted relative to that obtained in the molluscan matrix, indicating structural changes in the pigmentary molecules upon extraction. Published correlations were used to evaluate the possible length of the conjugated chain, and a new correlation was established using previous reported data. The conjugated chain length predicted from the new correlation of the studied pigmentary molecules ranges between ten and twelve double bonds. Copyright 2011, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Barnard, W 2006, A spectroscopic investigation of polyacetylenic molecules in the molluskan biogenic matrix, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-06262008-114600 / > E216/ag / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted