I could not tell directly if this was a ciliate or a dinoflagellate. As a ciliate, it would probably be a taxonomic relative of the genus Urocentrum. As a dinoflagellate, it would definitely be heterotrophic, as it lacks chloroplasts. The twirling characteristic does not give leverage to either hypothesis, as both the ciliates and dinoflagellates are known for twirling around as they traverse their watery biome.
I know have confirmation that this is, in fact, Urocentrum.