Final answer:
Dinoflagellates, or Pyrrophyta, have two flagella. One extends outward and wraps around a groove in the middle of the cell, while the other trails behind, giving them a spinning motion as they move through water.
Step-by-step explanation:
Pyrrophyta, also known as dinoflagellates, have two flagella. One flagellum extends outward from the cell and wraps around a groove in the middle of the cell, while the other flagellum trails behind. This flagellar arrangement gives dinoflagellates a characteristic spinning motion as they move through water.