The protist is about 2 to 4 μm long.Sunila, I. Dermo Disease. Oyster and Clam Diseases. Connecticut Department of Agriculture. The zoospore has two flagella, which it uses to swim in its marine habitat. It is ingested by its mollusc host, which is often an oyster of the genus Crassostrea. It then becomes a trophozoite, which proliferates in the tissues of the host. P. marinus often infests the hemocytes, cells in the blood of the host, analogous to malaria in vertebrates.Petty, D. Perkinsus Infections of Bivalve Molluscs. FA178. Fisheries and Aquatic Sciences. Florida Cooperative Extension Service. University of Florida IFAS. Published 2010. It is also often seen in the cells of the intestine, connective tissues, digestive glands, and gills. Inside the cell, the trophozoite produces a vacuole that displaces the cell nucleus. The infested cell is referred to as a signet ring cell, because it is spherical and filled with the rounded vacuole, and resembles a signet ring. The mature trophozoite undergoes binary fission and up to 16 immature trophozoites are produced. These stay in the host animal and infest its tissues, or are released into the water in the feces or from a dead host. Trophozoites in the water mature and release flagellated zoospores.
