Which of these groups includes photosynthetic unicellular organisms with flagella and contractile vacuoles?

Compare these features with the other groups: Diatoms are photosynthetic but lack flagella and contractile vacuoles; Dinoflagellates have flagella but typically lack contractile vacuoles; Ciliates have contractile vacuoles but are not primarily photosynthetic; Apicomplexans are parasitic and lack both flagella and contractile vacuoles.

Recognize that Euglenids are unique in combining photosynthesis, flagella, and contractile vacuoles, which matches the description given in the problem.