Morphological and cytological observations on two opalinid endocommensals of Acanthixalus spinosus (Amphibia, Anura)

Abstract

The morphology and cytology of two new opalinid species were studied using silver impregnation and fixation, which preserves the microfibrils. Both species, commensal on Acanthixalus spinosus, are host-specific. Light microscopy showed the existence of a posterior secant system in Opalina proteus n.sp. and its absence in Cepedea couillardi n.sp. (in agreement with the differences presently recognised between the two genera). At the ultrastructural level, however, both species present a posterior fibrillar zone that seems to be homologous with the secant system. This apparent contradiction may be explained by the fact that the secant system is visible under light microscopy only in O. proteus because its fibrillar zone is more developed than in C. couillardi. The life cycle of C. couillardi spans stages from the tadpole to the adult; in contrast, O. proteus completes its cycle before metamorphosis of the host.