Histology and histochemistry of the mantle of Pinctada radiata and Pinctada margaritifera from the Red Sea

Abstract

The mantle tissue of Pinctada radiate and Pinctada margaritifera of the Red Sea was examined both histologically and histochemically. Zonal variations having histochemical and histological significance were found in this tissue. These variations were used to define the different zones of the mantle and their relation to shell formation. A comparative analysis was performed between the two studied species and other species used in the pearl culture industry to emphasize the potential of Pinctada radiate and Pinctada margaritifera as candidates for pearl culture in the Red Sea. The periostracal material is secreted from the base of the periostracal groove from two specific area. Neutral, sulfated, and carboxylated polysaccharides are involved in the initial periostracal formation. Biochemical changes of the initial periostracal material occur while progressing along the groove and the periostracum become essentially sulfated. This change may be linked with the sclerotization process. The central zone is dominated by sulfated and neutral polysaccharides. The sulfated material is part of the shell organic matrix and is though t to concentrate calcium carbonate. Therefore, in Pinctada the central zone may be the major source of calcium and sulfated material necessary for shell construction. Central zone secretion is found above the pallial zone secretion suggesting that the central zone secretion under aerobic conditions may be the source of the calcium rich layer of the inner shell surface..