Distribution et importance quantitative de la chitine dans les coquilles de mollusques...peer reviewed1. The wide distribution of chitin in the shells of Molluscs was confirmed thanks to the application of a quantitative and specific enzymatic method. Chitin was found not only in Cephalopod shells, but also in mother-of-pearl, pseudonacreous layers, and in many cases, in periostracum and prismatic layers of Gastropod and Bivalve shells. 2. The presence and the proportion of chitin are highly variable in the periostracum of the Bivalve species studied so far. On the Contrary, its permanent presence in the organic matrix, associated with mother-of-pearl, emphasizes the homology of this structure in the whole phylum nof Mollusca. 3. The more or less important participation of chitin in the vbuilding of the organic matrix of the different shell structures may be related to taxonomic and/or ecological characteristics. From a taxonomical point of view, on the one hand, chitin distribution is in good agreement with the classification grouping Arcidae and Glycimeridae among the Filibranchia Taxodonta and isolating Nuculidae in the Protobranchia....
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