Summary
The ultrastructure of Cyclidium, including the cilia, kinetosomes, pellicle, microtubules and kinetodesmal fibers is similar to that recorded for other ciliates. Of special interest is the attachment of rod-shaped bacteria within the longitudinally directed shallow surface folds of the protozoan. Both the bacteria and the surface of Cyclidium seem to possess an outer coating of a sticky substance which upon contact holds the bacteria to the protozoan. The bacteria appear to be attached by only a relatively small area of their surfaces. A dense substance appears within the alveolus of the pellicle at the regions of the attachment of the bacteria. The association of the organisms is probably a temporary one, and it is unknown whether either organism is benefited or harmed by the association. The position of the mitochondria in Cyclidium is unusual in that they all lie flattened against the inner membrane of the pellicle, usually in a position directly opposite to that of the attachment of the bacteria to the surface, thus being separated from the bacteria by only the outer cell membrane and the pellicle. Whether or not this close topographical relationship is of significance is unknown.
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We are indebted to Dr. Dorothy Pitelka for help in determining the identity of certain membranes and microtubular structures in Cyclidium.
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Beams, H.W., Kessel, R.G. Studies on the fine structure of the protozoan Cyclidium, with special reference to the mitochondria, pellicle and surface-associated bacteria. Z.Zellforsch 139, 303–310 (1973). https://doi.org/10.1007/BF00306587
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DOI: https://doi.org/10.1007/BF00306587