Chlamydomonas belongs to the phylum

Chlamydomonas is a unicellular, microscopic, photosynthetic organism found in freshwater habitats. It possesses a cell wall, a cup-shaped chloroplast, an eyespot (stigma), and two flagella for locomotion. Because it is a simple, unicellular organism that can both photosynthesise and move, it is classified among the most primitive plant-like organisms.

In the traditional classification system used at WAEC/JAMB level, such simple, unicellular, plant-like organisms are placed in the phylum Protophyta (meaning "first plants"). This phylum includes algae and other simple photosynthetic organisms that do not have true roots, stems, or leaves.

The other phyla listed contain more complex organisms:

• Bryophyta includes mosses and liverworts, which are small, non-vascular land plants.
• Pteridophyta includes ferns and horsetails, which are vascular plants that reproduce by spores.
• Tracheophyta refers to all vascular plants (those with xylem and phloem), encompassing ferns, gymnosperms, and angiosperms.

Chlamydomonas lacks all of these complex features. Its unicellular, flagellated, photosynthetic nature places it firmly in Protophyta.