Until the 1980s, direct transmission of myxosporeans was presumed. In 1984, it was shown experimentally that spores of "Myxobolus cerebralis" failed to produce infections when fed to salmonids. To reproduce successfully, this species requires a tubificid worm as an intermediate host, in which the spores develop into a "species" of the "genus" "Triactinomyxon". These spores develop inside the oligochaete into forms which are infective to salmonids. Such a life cycle, with two different sexual stages, resulting in two kinds of resistant spores, is unique amongst the parasitic organisms. This mode of life cycle has been confirmed in several other "Myxobolus" species. This mode of infection has also been proved in other families. "Ceratomyxa shasta", an economically important parasite of salmonids, has been shown to use a polychaete worm as an alternate host.