4.2. Zoosporic hyperparasites

Zoosporic hyperparasites have been reported among Fungi in Blastocladiomycota, Chytridiomycota, and Cryptomycota, and among zoosporic fungus-like protists such as Hyphochytriomycota, Labyrinthulomycota, and Oomycota (Gleason et al., 2014), all three of which are now recognized as belonging to the Stramenopila lineage of Eukaryotes (Keeling and Burki, 2019; Wijayawardene et al., 2022). Zoosporic parasites can grow as epibionts on the surface of their hosts by means of specialized structures such as rhizoids, or as endobionts (i.e., intracellularly) being completely submerged within their hosts (Held, 1973, 1974; Gleason et al., 2012; Karling, 1960). There is a third type of association, such as in hyphal-forming zoosporic organisms, where interactions between hyphae of the hyperparasite and the primary parasite can be observed (Gleason et al., 2014). This is the case, for example, for the interactions of the oomycete Pythium oligandrum and hyphae of its plant-parasitic oomycete hosts, Pythium spp. and Phytophthora spp. (Benhamou et al., 1999).