Intranuclear Parasitism of the Ciliate Euplotes by a Trypanosomatid Flagellate

ABSTRACT A trypanosomatid flagellate, Leptomonas sp., develops and multiplies in the macronucleus (only) of natural and laboratory‐reared populations of the ciliate Euplotes. Up to 90% of the natural populations of Euplotes in our test pond had such nuclear infections. Laboratory infections were transmitted to this ciliate by feeding it liberated parasites. Paramecium resisted infections. All laboratory‐induced infections were lethal to Euplotes, while control clones of the uninfected ciliates remained viable. This leptomonad, unlike Leptomonas karyophilus (found in Paramecium), shows no leishmanial forms in its several ciliate hosts and shows a varied pattern of locomotion.