Mesodinium

Mesodinium is a genus of ciliates that are widely distributed and are abundant in marine and brackish waters.

Currently, six marine species of Mesodinium have been described and grouped by nutritional mode: plastidic (M. chamaeleon, M. coatsi, M. major, and M. rubrum) or heterotrophic (M. pulex and M. pupula). There is some debate as to whether the nutritional mode of plastidic Mesodinium species is phototrophic (permanent plastid) or mixotrophic. Among the plastidic species, wild M. major and M. rubrum populations possess red plastids belonging to genera Teleaulax, Plagioselmis, and Geminigera, while wild M. chamaeleon and M. coatsi populations normally contain green plastids. The availability of suitable cryptophyte prey is important for bloom formation of plastidic Mesodinium species.