Why are euglenas involved in polemics related to their taxonomic classification?

Euglenas are included in taxonomic polemics because they tend to be classified sometimes as protozoans and sometimes as algae. Although they have chloroplasts and they are photosynthetic autotrophic beings, euglenas do not have a cell wall and they can survive by "eating" substances from the environment when light is not available for photosynthesis. Curiously euglenas also have a photosensitive structure known as stigma that orients the movement of the cell towards light. Nowadays euglenas are classified as algae, but it is suspected that they are common ancestors of algae and protozoans.

Protists Review - Image Diversity: euglena