This infection affects oysters.

• A. Leech
• B. Microsporidia
• C. Dermocystidium marinum (dermo)
• D. Microbacteria

Answer: (C)

Oysters have a parasite-specific disease commonly known as dermo, caused by Dermocystidium marinum. This organism invades oyster tissues and creates white, nodular lesions on the mantle, gills, and surrounding tissues. Infected oysters may look normal initially but can suffer tissue damage, reduced growth, and higher mortality under stress or poor water conditions, which makes this disease particularly important in hatcheries and farms. Transmission happens through waterborne spores released by infected hosts or contaminated sediments, and warmer temperatures or high stocking densities can accelerate spread. Leech infections aren’t typical oyster pathogens, and while microsporidia and other bacteria can infect oysters, the classic infection most often linked to dermo is Dermocystidium marinum, which is why this option is the best answer.