AN OVARIAN PARASITE (PROTISTA INCERTAE SEDIS) FROM PACIFIC OYSTER CRASSOSTREA GIGAS

Examinations of the Pacific oyster, Crassostrea gigas, from Humboldt Bay, Calitornia, revealed an enigmatic parasite in the maturing ova during two successive years. Developmental stages occur primarily within prominent vacuoles in the cytoplasm of the eggs. The earliest stage observed resembles a uninucleate amoebula. Subsequent vegetative stages appear to develop primarily by successive divisions rather than from a distinct, multinucleate plasmodium. No mature spores are evident in the material. The organism differs in many respects from established parasites of bivalve molluscs, thus its systematic position remains problematical. It presumably belongs among the protozoa. Stages in the developmental cycle of the parasite are described and figured, staining and histochemical reactions are reported, and comparisons with other molluscan parasites are made. © 1969.