Final answer:
Dinoflagellates are unicellular protists with two flagella that allow them to move in a spinning motion. They can have a cellulose armor with grooves for the flagella and may produce toxins that cause 'red tides'.
Step-by-step explanation:
Dinoflagellates are a group of unicellular protists that exhibit a wide range of diversity in shape and size. These aquatic organisms are often recognized by their unique form of locomotion, which is facilitated by two flagella. Many dinoflagellates are encased in cellulose armor with intricate grooves where the flagella are located.
One flagellum extends longitudinally, and another encircles the organism, running perpendicular to the first. This arrangement of flagella in grooves between cellulose plates allows dinoflagellates to move in a spinning motion.
Dinoflagellates are commonly found as part of the plankton community in both freshwater and marine ecosystems and can be photosynthetic, heterotrophic, or mixotrophic.
Aside from their movement, some features that characterize dinoflagellates include the presence of a hard outer covering, known as a theca, in many species, and the formation of neurotoxins by some members. These neurotoxins can lead to paralytic shellfish poisoning in humans if they eat shellfish contaminated with the toxins.
Dinoflagellates may also cause a phenomenon known as 'red tides' due to population spikes and the presence of a red carotenoid pigment often found within these organisms.