Epibiosis is a facultative association between two organisms: the epibiont, which colonizes the surface of living substrates, and the basibiont, which hosts the epibionts. Among protists, while numerous accounts exist for ciliates as epibionts of zooplankton, little information is available about the occurrence of this relationship between flagellates and microcrustaceans in the neotropics. During a survey on the epibiotic relationship between ciliated protists and planktonic copepods in a tropical floodplain, we reported for the first time the occurrence of Colacium vesiculosum as an epibiont onThermocyclops minutus and Notodiaptomus amazonicus from southern Brazil. The mean infestation prevalence was significantly higher on adults 30.53% (± 2.85) in comparison with copepodites 0.87% (± 0.55). When hosts were separated by order (Calanoida and Cyclopoida) copepodites presented a mean infestation prevalence of 0.92% (± 0.85) and 0.83% (± 0.60) respectively, while adults had a mean prevalence of 29.55% (± 6.8) and 30.13% (± 5.83), which could be explained by the fact that adult copepods provide a more stable substrate for epibionts.
