Final answer:
Dinoflagellates characteristically possess two flagella which enable their unique spinning motion and are known for their role in aquatic ecosystems and for sometimes causing red tides and bioluminescence.
Step-by-step explanation:
Dinoflagellates are a group of unicellular protists that exhibit a great variety of shapes and sizes, with some possessing cellulose armor. They characteristically have two flagella which enable them to move with a spinning motion. The flagella fit into grooves between cellulose plates that make up the theca, one flagellum being longer and extending longitudinally, while the other is shorter and encircles the dinoflagellate.
This configuration contributes to the unique 'whirling' motion associated with dinoflagellates. Not only are they a crucial part of aquatic ecosystems as a component of plankton, but some species are also known for phenomena such as bioluminescence and red tides, which can have significant ecological and health impacts.