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Sphaeromyxa maiyai sp. n. (Protozoa:Myxosporidea) : a light microscopic and ultrastructural analysis employing the scanning and transmission electron microscopes Public Deposited

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  • Sphaeromyxa maiyai sp. n. (Myxosporidea:Myxiidae) is described from the gall bladder of the Pacific tomcod, Microgadus proximus Girard, from Newport, Oregon. The plasmodial (=trophic, trophozoite) stage is discoid averaging between 1 and 2 cm. The spore averages 27.6 x 5. 6μm with pyriform polar capsules averaging 9. 3 x 3. 7p,m. Sphaeromyxa maiyai was found to be nonpathogenic and produced no appreciable alterations in bile color or viscosity. In cross section the plasmodial stage consists of three distinct regions: a homogenous outer ectoplasm, a dense syncytial organelle containing endoplasm and a central organelle containing endoplasm and a central alveolar region. The ectoplasm and the mucous layer surrounding the exterior of the plasmodium are rich in acid mucopolysaccharides. The thick mucoid layer impeded observation of the ectoplasmic surface by scanning electron microscopy; however, ethylenediaminetetraacetic acid treatment removed the mucous and allowed partial visualization of the surface microvilli. Scanning electron microscopy of the spore revealed the presence of longitudinal striations and extruded polar filaments. The evagination of the polar filament is shown, By ultrastructural analysis the ectoplasm was shown to consist of a simplified homogenous zone composed of glycogen aggregates, scattered microtubules, pinocytotic vesicles and electron dense cylindrical bodies. The endoplasm constitutes the major organelle zone of the plasmodium. It was shown to be composed of vegetative and sporoblast nuclei, mitochondria, myeloid figures, smooth and rough endoplasmic reticulum, and scattered microtubules. Developing spores were found to consist of five distinct cells: two capsulogenic cells forming the polar capsules and polar filament, two shell valve cells forming the spore valves, and a single sporoplasm cell. The shell valves are joined at the sutural line by separate desmosomes. The polar filament was longitudinally folded within the polar capsule and contained four filament folds. The first coil differed from the remaining coils by being wider and thinner and having a wrinkled lumen. The filament matrix is composed of a homogenous electron dense material. The sporoplasm was centrally located within the spore and contained loboform extensions extending from the sporoplasm between the shell valve cells and the capsulogenic cells. Ultrastructural studies showing the complex polycellularity of the fully differentiated spore and the complex syncytial plasmodium containing polycellular aggregates of developing sporoblasts indicate the nonprotozoan character of the Myxosporidea.
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