Ultrastructure of Tuzetia weidneri sp. n. (Microsporidia: Tuzetiidae) in Skeletal Muscle of Litopenaeus setiferus and Farfantepenaeus aztecus (Crustacea: Decapoda) and New Data on Perezia nelsoni (Microsporidia: Pereziidae) in L. setiferus
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A new microsporidian species, Tuzetia weidneri sp. n. , is described from the skeletal muscle of the decapod crustaceans Litopenaeus setiferus and Farfantepenaeus aztecus. Fresh spores are pyriform, measuring 3.1 x 2.3 µm. All stages have unpaired nuclei. Meronts lie in direct contact with degenerate host cell cytoplasm but produce numerous small blisters at the surface. Multinucleate meronts divide by constriction into groups or chains of uninucleate products. Sporogony is initiated by deposition of a dense surface coat on the plasma membrane of uninucleate or multinucleate stages and fusion of blisters to enclose the sporont in a sporophorous vesicle (SV). Episporontal secretions in the SV are involved in the division of the sporont. During sporogonic division into chains of sporoblasts, the SV divides together with the body of the sporont, so that each sporoblast is enclosed in its own SV. Spores have a flattened anchoring disc that lies in the polar sac, membranous and spongiform regions of the polaroplast and 9-10.5 coils of the isofilar polar tube, around a posterior vacuole. The endospore layer of the spore wall is not thinned over the anchoring disc. The spore wall is adorned with a complex series of ridges. New data are presented on the spores of Perezia nelsoni (Sprague 1950) in L. setiferus. Of special interest is the polaroplast which is composed of an outer region of tightly-packed membranes in the form of a globule, which almost invariably completely encloses an inner region of loosely packed membranes. The isofilar polar tube, arranged in 8-10 coils angled around the large nucleus in the posterior half of the spore, passes through the membranes of the globular polaroplast near the periphery of the spore, then runs a curved course through the inner polaroplast and passes again through the globular polaroplast to join the anchoring disc. A polaroplast with one region completely enclosed by another has not been described previously.