Zoospores of the Oyster Pathogen, Dermocystidium marinum. I. Fine Structure of the Conoid and Other Sporozoan-Like Organelles

Abstract

An apical complex comparable to that found in the Sporozoa is described from zoospores of D. marinum Mackin, Owen and Collier, a pathogen of the American oyster (Crassostrea virginica Gmelin). The complex consists of a conoid, polar ring, up to 39 subplasmalemmal microtubules, rhoptries and micronemes. Micropores and a subpellicular membrane equivalent were also found. Acid phosphatase activity was found in cisternae of the endoplasmic reticulum, inclusion bodies and vesicles within the conoid lumen. No polysaccharides were detected in the rhoptries and micronemes using the Thiery method. Observations indicate that D. marinum is a protozoan in the subphylum Apicomplexa and is closely related to the coccidian Sporozoasida Leuckart.