Infection of the rainbow clam first intermediate host (Eurynia iris) has not been observed. It is likely, however, that the miracidia are swept through the incurrent siphon into the branchial chamber, where they attach to the gonad and burrow into it. Up to 6 percent of the clams from some areas are naturally infected. Branching sporocysts develop in gonads, often completely filling them. While only a single generation has been reported, it seems probably that a mother sporocyst and daughter sporocycst occur. Early development of the cercariae in the sporocysts is rapid but the time required for reaching maturity is unknown. They emerge from the gonads into the branchial chamber. Currents of water flowing from the excutten siphon carry them away from the clams. Upon reaching the outside, they spread the long furcae and hang with the body downward swimming slowly.
When the fish swim by, the furcae become entangled with the fins, holding the cercariae in a position that enables them to attach by the anterior holdfast and burrow into the tissues. As they work their way rapidly into the fins, the tail is discarded. Having entered the tissues, they move about, enlarging the space around them, and within an hour are enclosed in a hyaline cyst of parasitic origin.
Infection of rock bass takes place when fish harboring the cysts are eaten. Upon being released by the action of the digestive juices, the metacercariae migrate into the cecal pouches and mature in 30 days” (Olsen, 1974).