Dear student
Prior to 5 kingdom classification, Chlamydomonas and Chlorella were placed in kingdom plantae under Algae because both of them were having cell wall and chloroplast. But later on according to 5 kingdom, R.H Whittaker placed them in separate kingdom Protista which consist of unicellular eukaryotic organisms as they are mobile (through use of whip-like organelles called flagella).
Regards