Some parasites have evolved to grow on closely related host taxa. These parasites are known as “adelphoparasites” (Goff and Zuccarello, 1994). Species of Pythium are often parasitized by species of the same genus, such as P. acanthiumP. mycoparasiticumP. nunnP. oligandrum, and P. periplocum (Berry et al., 1993Deacon, 1976Deacon and Henry, 1978Lutchmeah and Cooke, 1984; Martin and Hancock, 1987Vesely, 1977). It is also common among chytrids to be parasitized by other chytrids. Species of the same genus may be both parasite and host and, in some cases, individuals of the same species parasitize each other (Frenken et al., 2017; Karling, 1960). For example, Chytridium parasiticum is a hyperparasite of Chytridium suburceolatum, which is itself a parasite on Rhizidium richmondense (Gleason et al., 2014; Willoughby, 1956). Adelphoparasitism is a common phenomenon among zoosporic hyperparasites, but it is also known in other taxa, such as in Tyrannicordyceps and Claviceps species (Kepler et al., 2012).
The most comprehensive taxonomic treatments on zoosporic hyperparasites were done by Karling (1942a, 1942b) and Sparrow (1960). More studies, however, are necessary to describe both the diversity of these organisms and their interactions.