Abnormal periostracum secretion during the mineralization process of the pearl in the blacklip pearl oyster Pinctada margaritifera

Whitish parasite-like bodies (PLBs), 0.5-2 mu m in size, were detected with in the pearl bag of some grafted pearl oysters, Pinctada margaritifera, fro m Takapoto island (French Polynesia). Histological and ultrastructural inve stigations have revealed that these bodies consisted of lamellar organic ma terial locally secreted by some epithelial cells of the pearl bag. The fine structure and the formation of these bodies are described. The causes of t his abnormal secretion of organic mater, which actually corresponds to peri ostracum, are not presently known. No parasite nor infectious micro-organis m was found associated with the PLBs. (C) 2000 Ifremer/Cnrs/Inra/Ird/Cemagr ef/Editions scientifiques et medicales Elsevier SAS.