Secondary spore formation in Orchesellaria mauguioi (Asellariales, Trichomycetes) and its taxonomic and ecological implications

Orchesellaria (Orc.) mauguioi (Asellariales) was detected from the hindguts of Isotomurus palustris (Collembola, Hexapoda) collected in Japan. The secondary spore formation on the exuviae of its host is described. When the host molted, its exoskelton including the ectoderm-originated hindgut cuticle to which Orc. mauguioi mycelia attaches was shed. Arthrospores of Orc. mauguioi germinated and penetrated the molt skin and produced secondary spores terminally. The secondary spore is a narrowly ovoid monosporangious sporangium accompanied by a capitate-lageniform terminal cell; these fall off together as a dispersive unit. The terminal cell is sterile and bears one to three fine filamentous extensions seven times as long as the length of the cell. In contrast to the appendages produced endogenously by other harpellids, the filament is produced exogenously and is similar to those of the genus Orphella (Harpellales). The taxonomic and ecological implications of the secondary spore formation of Orc. mauguioi are discussed by comparison with those of other Trichomycetes.