They have a complex life cycle that comprises vegetative forms in two hosts—one an aquatic invertebrate (generally an annelid but sometimes a bryozoan) and the other an ectothermic vertebrate, usually a fish.

In 1994 the phylum Myxozoa was redefined to solve the taxonomic and nomenclatural problems arising from the two-host life cycle of myxozoans.

Those remaining actinosporeans whose myxosporean stage is unattested are being retained as species inquirenda until their specific identity is established.

Such a life cycle—with two different sexual stages, each resulting in two kinds of resistant spores—is unique amongst parasitic organisms, let alone those in the kingdom of animals.

Ceratonova shasta, an economically important parasite of salmonids, has been shown to use a polychaete worm as an alternate host.