Ultrastructural study of Euplotidium itoi (Ciliata Hypotrichida).

Details of the cortical, cytoplasmic, and nuclear ultrastructure of Euplotidium itoi are provided here for the first time. When these ultrastructural characteristics are compared with the corresponding features of representative members of the family Euplotidae, it arises that the differences between E. itoi and these individual taxa fall into the range of variability of the family. As reported elsewhere [29] E. itoi harbors peculiar epibionts (epixenosomes) inserted in a sort of band running along the margins of its dorsal surface. A detailed analysis of the cortex at the level of the epibiont band revealed the constant presence of parasomal sac-like vesicles not associated with ciliary structures. As these vesicles are present only at this level, it can be supposed that they have an important role in the relationship between E. itoi and the epixenosomes.