Unikaryon montanum sp, n. infects the fat body, muscle, Malpighian tubules and ovaries of adult Ips typographus L. The development is haplokaryotic, with separate nuclei during the schizogony and sporogony. Sporonts have the cellular envelope with added layer of electron dense material. Two types of spores are formed: small broad-oval primary spores, 1.5 x 1.0 pm, with warty surface of spore wall, uninucleate, with isofilar polar filament in 5/6 coils and elongated-oval environmental spores, 0.8-1 x 2 pm, with warty spore wall attenuated at the anterior end, uninucleate, with spore polar filament in 8 coils. Both types have a dual polaroplast with the anterior part of a layer of confluent fine lamellae ending posteriorly in bulbous processes, and posterior part composed of coil of tubules.