Functional morphology of the coelomocytes of the larval oysters ( Crassostrea virginica and Crassostrea gigas )

The functional morphology of the coelomocytes of larval oysters, Crassostrea virginica and C. gigas , based on observations of live animals and histological and ultrastructural examination of tissues, is presented. Two predominant types of coelomocytes were found in the larval oysters. One, the SER cell, not found in the adult oyster, is large with a spheroidal nucleus, and exhibits basophilic cytoplasm which consists of abundant smooth endoplastic reticulum. This cell appears to participate in metabolic conversion processes. The other predominant cell type, the phagocyte, appears identical to the phagocyte observed in the adult oyster. Both differential cell types were observed from one day post fertilization to metamorphosis, the oldest stage studied.