This colorized scanning electron microscope (SEM) image depicts the shell of a young Crassostrea virginica oyster affected with juvenile oyster disease. This disease is responsible for considerable mortalities of farm-raised Eastern oysters every year. Up to 90% of juvenile oysters expire and the aquaculture industry in the northeast is seriously and financially impacted by this incurable disease. Conchiolin, the yellow stringy material in the image, is a hallmark of JOD infection. In live oysters, conchiolin resembles a brownish fleshy organic material that is found on the inside surface of the shell. Conchiolin has a putative role in molluscan immunity and is thought to be created by the oyster in an attempt to protect vulnerable tissue. Oysters often respond to a foreign pathogen by creating a wall of shell and organic material around the pathogen. This encapsulation response is driven by hemocytes, oyster blood cells, which aggregate around the intruder and deposit calcium carbonate crystals.