Final answer:
The protists in question are dinoflagellates, which are notable for their two flagella, cellulose plates, and some producing bioluminescence or toxins.
Step-by-step explanation:
Protists that possess two flagella, plates made of a cellulose-like material, and may be bioluminescent or produce toxins are dinoflagellates. These diverse organisms can be phototrophic, heterotrophic, or mixotrophic, and their chloroplasts originated from a secondary endosymbiosis with a red alga. With a characteristic spinning motion due to their two flagella, dinoflagellates can be found as a vital part of the plankton community in both fresh and saltwater ecosystems. While many have protective cellulose plates, known as theca, some species are notable for their ability to produce neurotoxins harmful to humans and marine life alike.