This paper presents the results of observations on the curious flagellum found in ephemeral water bodies during their algological studies in 2000–2014. Morphologically revealed specimens are close to species of rare genus Myochloris J.H.Belcher & Swale (Prasinophytina, Chlorophyta). However, a detailed study of the cellular structure of this flagellate, as well as observation of its behavior in fresh algological samples, made it doubtful that this is a phototrophic organism. We have repeatedly observed its aggressive behavior: this active predator (algophagus) attacked the cells of algae, joined them with the front pointed сell end and completely sucked out their contents. Comparison of the morphology of this flagellate with protists allowed us to identify this organism as Colpodella s. l. (Apicomonada, Apicomplexa, Alveolata, Chromista). The features that were previously described as attributes of a phototrophic organization in the cell of flagellate are in fact digestive vacuoles at an early stage of digestion. The high morphological variability of these structures (the number of stigmae, pyrenoids, morphology of the "chloroplast") confirms this assumption. Thus, we propose to consider the species from the genus Myochloris as synonyms for Colpodella s. l. Comparative characteristics of Myochloris and Colpodella s. l. based both on literature data and our observations of the flagellates revealed are given. Original micrographs and figures are provided. Diversity, structure and phylogeny of Colpodellida as well as their role in water ecosystems are discussed.
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