The morphology of an isolate of parasitic ciliate Cryptocaryon irritans obtained from cage-cultured snubnose pompano （Trachinotus blochii）from Huidong, Guangdong Province in China, was examined by observation of scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The strains were maintained in experimentally infecting snubnose pompano from which the sample used for ultiastructural observation was collected. The general structural organization of the pellicles resembles that of the freshwater holotrich lchthyophthirius multifiliis, consisting of three membranes： outer limiting membrane, the outer alveolar membrane and the inner alveolar membrane. The pellicular alveoli are characterized by the accumulation of election dense material in the trophont, tomite and theront, this material being lost in the newly-encysted tomont. The theront, tomite and tiophont possess a complex oral apparatus, being composed of cytopharynx, oral rib, dikinetids and nematodesmata, without an organelle of Lieberkuhn which is considered as a synapomorphy of the suborder Ophryoglenina. The monokinetid somatic cilia appear in rows longitudinally on the theronts, tomites and trophonts, but being lost at early stage of tomonts. There are mitochondria, Golgi apparatus and lipid droplets in the cytoplasma of all stages of parasite, and mucocysts, contractile vacuoles and endosymbiotic bacteria in theronts and trophonts. The size, shape and distribution of mucocysts in C. irritans are different from thoseof I. multifiliis. The present study suggests that the taxonomic affinities of C. irritates should lie with prostome ciliates by analysis of its different morphological characteristics from I. multifiliis.