Muscle system in rediae and daughter sporocysts of several digeneans.

Morphological studies on digenetic trematodes are quite numerous, but the large majority of researchers deal with the hermaphroditic generation (cercariae, metacercariae, adults). Parthenitae (miracidia, sporocysts, rediae), although they constitute a significant part of a digeneans' life cycle, attract much less attention. The sparse literature concerning the musculature of parthenitae indicates that it differs in many respects from that of digenean hermaphroditic generation and many other flatworms. We have tried to fill the knowledge gap on digenean muscle systems by focusing on daughter parthenitae (three species with rediae and two with daughter sporocysts). The study was performed using TRITC-phalloidin labeling and confocal microscopy and was aimed at both describing general trends and comparing different morphotypes. The basic body-wall muscle layers were confirmed to be composed of circular and longitudinal muscle fibers. Circular fibers form quite a uniform layer, and longitudinal fibers are typically joined into bundles. The density of muscle layers varies widely among studied species, and the possible causes of this variation are discussed. The internal muscle fibers and bundles are present in all studied species, being most prominent in the anterior region. The brood chamber and birth pore channel often have a muscular lining. The rediae pharynx has a typical set of muscle elements, mostly coinciding with one in the pharynx of the hermaphroditic generation. Taken together, our findings suggest that data on the musculature of daughter parthenitae are important from an evolutionary perspective. [ABSTRACT FROM AUTHOR]