Abstract
Two new species of ciliates parasitizing marine molluscs in the Yellow Sea were described using live observation, protargol and wet silver impregnation: Sphenophrya solinis sp. nov. from the gills of Solen grandis and Planeticovorticella paradoxa sp. nov. from the gills as well as the mantle cavity of Meretrix meretrix. Sphenophrya solinis is elongate boat-shaped, and characterized by having the right system of 5-6 kineties more or less distinctly longer than the left system of 3-5 kineties and the bud formed on the dorsal left of body during budding. Planeticovorticella paradoxa is a second member of the genus Planeticovorticella, and characterized by the free-swimming, cylindroidal trophonts usually with no stalk or with a very short and non-contractile stalk, the C-shaped macronucleus longitudinally oriented in mid-body, and the apically located contractile vacuole. The morphology, infraciliature and morphometry of the two new species were studied in detail and compared with those of their most similar congeners.