Haplosporidium costale (Sporozoa) Associated with a Disease of Virginia Oysters.

A new species of Haplosporidium is reported as the cause of a previously unrecognized disease of Crassostrea virginica (Gmelin) on the Eastern Shore of Virginia. The species is characterized by small (3.1 by 2.6 micro) operculate spores without projections. Infections are first seen in late winter, and mortality reaches its peak in early June.