FlagellumA long whip at the front end. It beats to move the cell through the water. A second, short flagellum never leaves the reservoir.
Eyespot (stigma)A patch of pigment granules near the front. As the cell turns, it shades the photoreceptor, which helps the cell find the light.
ChloroplastsThey make food for the cell from light. Each holds chlorophyll, as the chloroplasts of a plant do.
NucleusOne nucleus lies near the middle of the cell. It divides first when the cell splits in two.
Contractile vacuoleA round sac that collects excess water. It empties into the reservoir, and the water leaves the cell from there.
PellicleA flexible coat of protein strips, not a cell wall. The strips slide past one another, so the cell can change its shape.
The front end 2
ReservoirA pocket in the cell's front. Both flagella rise from its floor, and the contractile vacuole empties into it.
PhotoreceptorA swelling near the base of the long flagellum. It is the part that detects light, and it is also called the paraflagellar body.
The rest of the cell 1
Paramylon granulesGrains of stored food. Paramylon is a carbohydrate like starch, built from the sugar the chloroplasts make.
How this list was compiled: Every name was checked on 2026-10-01 and kept only where two independent sources use it for Euglena. (1) Wikipedia, text only: Euglena, https://en.wikipedia.org/wiki/Euglena . (2) R. W. Hegner, College Zoology (1912), the section on Euglena viridis, public domain, https://archive.org/details/collegezoology00hegn . (3) George M. Briggs, Inanimate Life, the chapter on Euglena, an open college botany textbook, https://milnepublishing.geneseo.edu/botany/chapter/euglena/ . (4) Two journal abstracts and one open-access paper on how Euglena finds light, read through Europe PMC: https://europepmc.org/article/MED/31630463 , https://europepmc.org/article/MED/28429324 and https://europepmc.org/article/PMC/PMC8911436 . Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
This euglena cell diagram shows the cell cut open, front end up. Tap a name to read what the part does, then press Quiz me.
Read the full guide
Start at the front end
The long flagellum leaves the cell through the neck of the reservoir. The eyespot sits beside that neck, and the photoreceptor is the swelling on the flagellum just inside. The contractile vacuole touches the reservoir and empties into it.
Then the rest of the cell
The pellicle is the striped coat all round. Inside are the oval chloroplasts, the smaller paramylon granules between them, and one large nucleus.
The eyespot is not thought to sense light itself. It shades the photoreceptor next to it.
A Euglena has no cell wall. Its pellicle bends, so the cell can change shape.
Questions and answers
What are the parts of a euglena cell?
A long flagellum, a reservoir it rises from, an eyespot, a photoreceptor, a contractile vacuole, a pellicle in place of a cell wall, chloroplasts, paramylon granules and a nucleus.
Is a euglena a plant or an animal?
Neither. It is a single-celled organism that both botanists and zoologists once claimed: in light it makes food by photosynthesis, as a plant does, and it swims and can take in food from the water without light.
What does the eyespot do in a euglena?
It is a patch of pigment granules beside the reservoir. As the swimming cell turns, the eyespot shades the photoreceptor at the base of the flagellum, and the cell uses that to steer toward light.
What does the contractile vacuole do in a euglena?
It collects excess water and empties it into the reservoir, the pocket at the front of the cell, so the water leaves the cell.