It’s a genus of trematodes, including several species parasitic in the blood of humans and domestic animals. The organisms are called schistosomes or blood flukes. Larvae (cercariae) enter the body of the host by way of the digestive tract, or through the skin from contact with contaminated water, and migrate in the blood to small blood vessels of organs of the intestinal or urinary tract; they attach themselves to the blood vessel walls and mature and reproduce. The intermediate hosts are snails of various species.

Blood-flukes. Flatworm parasites. They can live in you for decades. Pretty cool!