The pellicle is a flexible, protein-rich layer that lies just beneath the cell membrane of Euglena. It gives Euglena its characteristic shape and allows it to change shape (being able to move by wriggling or gliding). This is a key characteristic that differentiates Euglena from true plants.

Here's why:

* True plants have rigid cell walls made of cellulose. This provides structural support and gives them their characteristic shape.

* Euglena's pellicle allows for flexibility and movement. This is essential for their ability to move through their aquatic environment.

While Euglena does contain chloroplasts and can photosynthesize, they are also capable of heterotrophic nutrition, meaning they can consume other organisms for food. This further distinguishes them from true plants, which rely solely on photosynthesis for energy.

Therefore, the flexibility and protein composition of the pellicle is a key characteristic that separates Euglena from true plants.