Schistosoma mansoni eggs, miracidia and primary sporocysts were labelled with phalloidin-rhodamine to visualize filamentous actin structures. Analysis of these forms by confocal fluorescence microscopy revealed the presence of previously well-defined circular and longitudinal muscle layers. Besides these muscular layers that sustain and provide motility to these parasite forms, we found in these 3 consecutive developmental stages of the parasite previously unidentified actin-rich tubular structures. In the 3 forms, 4 actin-rich tubules could be observed by optical sectioning underneath the well-developed muscle layers. The tubules appear in pairs, transversal to the length of the parasite, and located towards the extremities. By using an anti-flame cell specific antibody we confirmed that the tubules co-localize with flame cells and also determined that the tubule core is filled with microtubules. The additional presence of myosin in these tubules strongly suggests that they are contractile structures.
