The
Myxosporea are a
class of microscopic
parasites, belonging to the
Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic
invertebrate (generally an
annelid) and an
ectothermic vertebrate, usually a
fish. Each host releases a different type of
spore. The two forms of spore are so different that until recently they were treated as belonging to different classes within the Myxozoa.