Comparative ultrastructure of the actinosporean stages of Myxobolus brarnae and M. pseudodispar (Myxozoa)

The ultrastructrure of triactinospores and other developmental stages obtained after the experimental infection of the oligochaete Tubifex tubifex with myxospores of Myxobolus bramae and Myxobolus pseudodispar was studied. In both cases, pansporocysts harbouring spores and the remnants of polar bodies were found in the gut epithelium of the tubificids. Other stages were also seen in M. pseudodispar. Capsulogenic cells surrounded the apical part of the sporoplasm in M. bramae whereas they were located separately in M. pseudodispar. The sporoplasm of M. bramae was elongated and was filled with numerous infective cells, whereas secondary cells rarely appeared in the sporoplasm of M. pseudodispar, which contained large groups of β-glycogen granules. Other M. pseudodispar stages included pansporocysts harbouring pregametic or gametic stages, zygotes, or the initial steps of sporogenesis. The presence of first- and second-order polar bodies indicates the existence of meiosis. In the spores of M. pseudodispar, the presence of desmosome-like junctions between the capsulogenic cells, and hemidesmosome-like junctions between the capsulogenic cells and the inner membrane of the valvogenic cells, is remarkable.The authorswish to acknowledge the CSIC – Hungarian Academy of Sciences Agreement for supporting this work. We are grateful to techniciansfrom the Electron Microscope Service of the University of Barcelona for TEM processing. Additional financial help wasprovided by research grant MAR98/ 1000 from the Spanish CICYT and contracts T 029200 and T 031755 from the Hungarian Scientific Research Fund (OTKA). The authorsalso declare that all the experimentscomply with the current lawsof Hungary, where the experimental infectionswere performed