Ultrastructural Aspects of the Somatic Cortex and Contractile Vacuole of the Ciliate,Ichthyophthirius multifiliis Fouquet1

The trophont stage in the life cycle of Ichthyophthirius multifiliis was studied in the electron microscope. Surface ridges contain up to 24 ridge microtubules, disposed as a ribbon. Kinetosomes show the classic morphology of 9 triplets of microtubules. Associated with each kinetosome is a kinetodesmal fibril, originating in proximity to triplets 5, 6, and 7, and having a 30 nm periodicity; 3 to 5 postciliary microtubules, originating between triplets 8 and 9; and up to 3 transverse microtubules, originating at triplet 4, as well as a parasomal sac. Each cell is partially enclosed by a system of 3 “unit” membranes: the outer limiting membrane, and the outer and inner alveolar membranes. The last two membranes define the alveolar sac. Mucocysts, each with a dense core, are present in large numbers. The contractile vacuole system includes the contractile vacuole, associated tubules and vesicles, injection canals, a discharge canal, and a pore. Microtubules abound in the walls of the contractile vacuole, injection and discharge canals, and in the region of the pores, where both ring and radial microtubular arrangements are noted. The ultrastructure suggests that I. multifiliis is more closely related to Tetrahymena pyriformis than to Paramecium aurelia.