Development of Myxobolus dispar (Myxosporea : Myxobolidae) in an oligochaete alternate host, Tubifex tubifex

The development of Myxobolus dispar Thelohan, 1895, a myxosporean parasite of the gills of common carp (Cyprinus carpio L.) was studied in experimenta lly infected oligochaetes Tubifex tubifex Muller. After infection of uninfe cted tubificids with mature spores of M. dispar development of actinosporea n stages was first observed light microscopically 21 days after initial exp osure. In histological sections, early pansporocysts were located in the gu t epithelium of experimental oligochaetes, while advanced stages occupied m ostly the outer layers of the gut and the coelozoic space. Mature pansporoc ysts, each containing 8 raabeia spores, appeared 199 days after initial exp osure. Following damage of the intestinal wall and rupture of the pansporoc ysts, free actinosporean stages were found in the gut lumen of the oligocha etes. Actinospores of M. dispar emerged from the worms after 217 days of in tra-oligochaete development. They were floating in the water and showed a u nique raabeia form. Each raabeia sport had three pyriform polar capsules an d a cylindrical-shaped sporoplasm with approximately 32 secondary cells. Th e spore body joined the three caudal projections without a style. Caudal pr ojections were bifurcated at the end and the two main branches had further small bifurcations. The total length of the raabeia sport was approximately 158 mu m. The prevalence of infection in 240 experimentally infected Tubif ex specimens was 99.2%. No infection was found in the control oligochaetes.