Ciliatosporidium platyophryae nov. gen., nov. spec. (Microspora incerta sedis), a parasite of Platyophrya terricola (Ciliophora, Colpodea)

Summary Ciliatosporidium platyophryae nov. gen., nov. spec, is a microsporidian parasite affecting the soil ciliate Cirrophrya terricola Foissner, 1987. It was found in a soil sample from Utah (USA), pure cultures were not available. The developmental stages seen are uninucleate and divide by binary fission (disporoblastic). Each sporont is enveloped by a membranelike exospore precursor and a parasitophorous vacuole deriving from host endoplasmic reticulum and persisting during spore maturation. The spore is rod-shaped with hemispherical ends and measures about 4×2 μm. It has a short, uncoiled polar filament and conspicuous, possibly transient sacs in the wide anterior lamellae of the bipartite polaroplast. The exospore has the appearance of a unit membrane. Maturing spores induce the formation of appendages (“feet”) at the posterior end of the host which was thus formerly assigned to the genus Cirrophrya . However, our study shows that the feet are a pathological phenomenon and the host thus belongs to the genus Platyophrya: Platyophrya terricola (Foissner, 1987) nov. comb. Despite its unusual host, the fine structure of C. platyophryae is very similar to that of microsporidia from other invertebrate and vertebrate hosts. Very likely, C. platyophryae is related to the genera Oligosporidium, Encephalitozoon, Unikaryon and Endoreticulatus , presently assigned to the families Encephalitozoonidae and/or Unikaryonidae. However, for a definite classification of C. platyophryae more detailed data on its life cycle and membranous envelopes are necessary. Thus, we prefer an incerta sedis position.