Whirling Disease: Spores
The whirling disease parasite, Myxobolus cerebralis, forms small spores like this one, photographed with an electron microscope. The spores remain viable for dozens of years in the mud, until they are eaten by a small worm known as Tubifex tubifex. When the worms die, they release another phase of the parasite known as a triactinomyxon (TAM) that is ready to infect another fish and complete the life cycle.
Photo by Ronald P. Hedrick