Ceratium Schrank is a planktonic dinoflagellate ubiquitous in temperate and subtropical freshwater environments from Northern Hemisphere. Over the past two decades, Ceratium species have been recorded in South American water bodies, with expansive behavior and fast colonization. This study registered C. furcoides (Levander) Langhans and C. hirundinella (O. F. Müller) Dujardin for the first time in South Brazil. Ceratium furcoides was found in samples from States of Paraná and Rio Grande do Sul and C. hirundinella occurred only in the southernmost Brazil. No co-occurrence of these species was detected on samples. The morphological variation, as well as the dispersal patterns of these species in Brazilian environments, is discussed based on LM and SEM analyses.