Pleistophora Gurley 1893

Monomorphic, monokaryotic throughout life cycle; merogony with multinucleate plasmodia with a thick amorphous coat, permeated by channels, division is by plasmotomy into smaller segments, the amorphous coat dividing at the same time; sporogony is polysporous within a sporophorous vesicle, formed by separation of the amorphous coat from the surface and modification of the coat by inclusion of further electron dense material secreted by the sporont; sporogonial plasmodia have many nuclei; after secretion of a new surface coat, the plasmodium divides sequentially into smaller pieces, eventually producing uninucleate sporoblasts and microspores; rarely only 8 sporoblasts are formed, which give rise to macrospores; spores microspores, 4.4 x 2.3 µm, are ovoid and uninucleate; exospore is thin, endospore thick; polaroplast is lamellar, with an anterior region of closely packed membranes and posterior region of loose sacs; polar tube is isofilar with 10-22 coils in 1-3 ranks; prominent posterior vacuole; macrospores, 7.4 - 3.0 µm, have the same morphology as microspores except that the number of coils of the polar tube is greater, up to 33; parasites destroy the muscle fibres and lie in spaces adjacent to myofibrils; type species P. typicalis Gurley, 1893 in striated muscle of Myoxocephalus (Cottus) scorpius (Pisces, Cottidae).