ABSTRACT
Light microscopy revealed epizoic thigmotrich ciliates and pennate diatoms living on triphyllous pedicellariae. No other type of pedicellariae was infected. Thigmotrichs occurred on triphyllous pedicellariae in Echinus esculentus Linné, and Psammechinus miliaris (Gmelin), nestling in the concavity of the inner jaw surfaces. The infection level was higher in P. miliaris than in E. esculentus. Light microscopy as well as transmission and scanning electron microscopy were used to investigate the relationship between ciliates and pedicellariae, A number of evacuolated cell fragments were seen in the ciliate cytoplasm. These could have come from echinoid epithelium or prokaryote material available to triphyllous pedicellariae. E. esculentus alone harboured diatoms which were attached to exposed areas of skeletal calcite, probably taking advantage of unexploited substrate.
