(Euglena Facts) – 10 Fascinating Facts About Euglena In Detail

Share This Post & Help Others!

Euglena genus includes more than 1,000 species of single-celled flagellated microorganisms that are included under the classification of small protozoans (Phylum Protozoa) in the books of Zoology.

Euglena features both plant and animal characteristics, and so they are neither plants nor animals. Better to refer to them as partial plant or partial animal species.

They are found worldwide and are both freshwater and saltwater species depending on the habitat type. They remain fairly active and are often found at various depths below the surface of the water.

You will often find them abundantly above the surface of stagnant water bodies like ponds, showing a green film-like appearance on the water surface.

Find Out More About These Amazing Small Plant-Animal Like Protozoans That Are Solitary And Free-living Freshwater/Saltwater Flagellates.

Here Are The 10 Fascinating Facts About Euglena You Must Know About. Let’s Know

1. Euglena has a red eyespot

The eyespot (eye-like marking) of Euglena is also known as the stigma and is red in color due to the presence of a red-colored pigment named carotenoid.

The eyespot is a cup-shaped red-pigmented spot located near the reservoir at the gullet part at the base of the flagellum. That is the location is on the opposite side of the contractile vacuole.


This eyespot is actually a membrane-bounded organelle that doesn’t have any homology with the green chloroplast or any other organelle.

The advantage of having this eyespot is to perform phototaxis by Euglena. This helps the euglena find bright areas to gather sunlight to make their food as autotrophs.

It is also to be noted that the Euglena avoids strong lights as well as shady areas, but in fact, it stays and reacts positively to a moderately intense light such as that coming from a window or ventilator.

It is also seen that the Euglena orients itself parallel to a beam of light coming towards it and swims towards the source of illumination for performing photosynthesis. That’s possible due to the eyespot.

It is to be noted that the red pigment of the eyespot is not photosensitive at all.  But, it has been noticed that when sunlight falls at the base of the flagellum, the red pigment filters out the light allowing only certain wavelengths of light to reach it.

2. They are both autotrophs and heterotrophs

Eating in Euglena is more like consuming (absorbing). In fact, they consume (absorb) the sunlight to produce food autotrophically.

Or, they use their Pellicle to consume (absorb) dead organic matter to produce food saprophytically by pinocytosis.

So, they are considered as both autotrophs and heterotrophs.

They are called autotrophic organisms as they can produce their own food with the help of photosynthesis using their chloroplasts.

And when there is no light, they can also depend upon the other living organisms as saprophytes by feeding on organic dead and decaying matter by absorbing it from the surrounding water using their pellicle.

So, using Chloroplast they produce food from sunlight, water, carbon dioxide, or other chemicals. And, by using their Pellicle they derive their food from dead and decaying matter.

When the Euglena feeds using the cell surface pellicle, it surrounds the food particle and consumes it by phagocytosis, or in other words, by engulfing the food through its pellicle layers and then takes it inside through the cell membrane.

READ MORE: How does Euglena eat? (Nutrition in Euglena)

3. It can survive in both fresh and salt water

Depending upon the species, they can live in freshwater or saltwater. Some species can live either in freshwater or saltwater and some have evolved to live in both.

You will find them in inland waters, stagnant water bodies, coastal water regions, and even in the deep-sea regions. They do abundantly bloom in numbers sufficient to the color of green or red on the surface of ponds.

Then can stay in saltwater and in regions of wet conditions with less amount of water as well.

In low moisture conditions, Euglena forms a protective wall called a cyst around itself and lies dormant as a spore until environmental conditions get better and moisture increases.

It has been seen that the species of Euglena occur in freshwater ponds, pools, ditches, and in slowly-running streams where there is a considerable amount of vegetation.

It can also be found at various depths below the surface of the water. Can also be seen in water bodies like ponds where there is decaying nitrogenous organic matter, such as feces of animals, leaves, twigs, etc.

4. They can also survive in the dark

Yes, they can also survive in the dark by heterotrophically deriving their nutrition from the decaying organic matter in the water body.

Saprophytic or Saprozoic Nutrition is performed by those Euglena species that have lost their chlorophyll due to its living in the regions of prolonged darkness.

Like for example, due to staying inside the rocks, under the shade in any aquatic environment where sunlight couldn’t penetrate.

Due to the absence of chloroplast, the Euglenas’ body becomes pale or white in colour, yet it continues to live and perform all of the life activities. So, they perform Saprophytic or Saprozoic Nutrition which is a type of Heterotrophic nutrition.

Some Euglena species can get nutrition by both autotrophically and heterotrophically. They use chloroplast in the presence of sunlight, and use their pellicle in the absence of sunlight.

They are also able to survive in the dark because they are not so strictly phototaxis (reacting to sunlight).

5. Euglenas are neither plants nor animals despite the fact that they have characteristics of both

Yes, Euglena is studied under both Botany and Zoology as it finds its applications under both botanical and zoological studies.

These microscopic organisms show both the partial characteristics of plants and animals and so can’t be considered either as true plant or animal.

And so, they can be well-classified under the Kingdom Protista. Phylum Protozoa comes under the Kingdom Protista with other Phyla like Protophyta, Protofungus, etc.

The Protozoans (singular: Protozoa) are Animal-like protists that were understood to be animals and so often termed as animalcules and so they are studied in the Departments of Zoology.

However, animalcules like Euglena are those protozoans that are both animal-like and plant-like. So they are studied in both the Departments of Zoology & Botany.

Euglena shows plant-like characteristics due to the presence of chloroplasts and due to performing autotrophic nutrition. Being positively phototactic due to the eyespot is another reason.

Euglena shows animal-like characteristics due to the absence of cellulose cell-wall, presence of centrioles, presence of paramylon (not true starch), due to performing saprophytic nutrition, and also because it can move from place to place like an animal.

ALSO READ: Are Protozoa and Protista the same thing or different? – (ANSWERED)

6. They do respond to the environment by showing reaction to light, by shock reaction, and also by avoidance reaction

It has been seen that like other protozoans, Euglena too moves and responds to various stimuli like light stimuli, mechanical stimuli, thermal stimuli, and chemical stimuli with a wide variety of orientations and movements.

As they don’t have eyes like sense organs, their way of reaction, movement, and responding to the surrounding stimuli is highly dependent based on the use of the various cell organelles. One of such important stimuli is the light stimuli detected using the red eyespot.

Euglena shows a reaction towards sunlight. That’s positive phototaxis and so, it stays and reacts positively to a moderately intense light such as that coming from a window or ventilator.

When the sunlight is available, they can detect the light using their eyespot and eventually moves toward the light by phototaxis (reaction to light). The sunlight is trapped by chloroplasts within the euglena for photosynthesis purposes.

Euglena also shows a shock reaction, when the direction of the sunlight suddenly changes. Meaning that Euglena will be shocked for a while and will not get the proper stimulus of its direction of movement, and so with trial and error, it will soon detect the new direction of light and will flow towards the new direction.

Euglena also responds to mechanical, thermal, and chemical stimuli showing an avoiding reaction on a trial and error pattern. This is known as phobotaxis.

Avoiding reaction is actually a random behavioural response that causes strong dislike or disinclination towards aversive stimuli thus helping Euglena to avoid obstacles.

READ MORE: How does Euglena respond to the environment? – (Behaviour of Euglena)

7. They move by showing both Flagellar Movement and Euglenoid Movement

Yes, Euglena shows both types of movements, viz. the Flagellar movement and Euglenoid Movement.

Flagellar movement is by the use of flagella to turn and twist in the water, while the Euglenoid movement is by the use of pellicle to produce peristaltic movement.

During the flagellar movement, Euglena uses flagella to create a propulsion mechanism just like a propeller of a boat to move the body forward in the water.

There is only one locomotory flagellum at the anterior end of the Euglena, and it’s almost equal to the length of the Euglena.

The movement of the flagellum involves the continuous contraction of its 9 peripheral fibres using the ATP energy of the cell.

While the Euglenoid Movement is usually possible due to the presence of flexible pellicle in the surface of their body which causes peristaltic movements causing to alter the shape of their body and then come to their real shape just like an elastic rubber band.

READ MORE: How does Euglena move? (Locomotion & Movement in Euglena)

8. Euglena’s chloroplasts are surrounded by three membranes

One interesting thing to note is that the chloroplasts in Euglena are surrounded by three membranes, while those of the plants and the green algae have only two membranes.

It is proposed that the third membrane of the chloroplast has been evolved from the progressive reduction of endosymbiotic green algae’s plasma membrane layer.

9. Euglena lacks a cell wall, instead, it has a pellicle

Yes, the cell wall is absent in Euglena. This gives it the animal-like classification.

Instead, the pellicle layer is present on the cell surface of Euglena just beneath the cell membrane. This layer is made up of protein layers of microtubules, arranged in strips spiraling around the cell.

This pellicle actually helps in the peristaltic movement of Euglena done by the sliding of the pellicle strips in the grooves between the strips which is further lubricated by the secretion of underlying muciferous bodies.

Electron microscopy study shows that each pellicular strip has an elaborate cross-sectional shape showcasing various accessory teeth, ribs, and a continuous ridge that articulates in a groove running along the edge of the next strip.

In simple words, the pellicle consists of flat strips of material that pass along the cell in a helical manner.

The edges of adjacent strips overlap and articulate along their entire length in such a way that the ridge of one fits into the groove of the other. This articulating edges appear as striations called myonemes on the cell surface of Euglena.

It is to be noted that the pellicle layer is actually made up of proteins, and not cellulose, and so that is not homologous to the plant cell wall.

10. Euglena reproduces asexually using the processes of longitudinal binary fission and multiple fission

Euglena reproduces asexually using the processes of longitudinal binary fission and multiple fission only.

In longitudinal binary fission, Euglena divides mitotically in the axil or longitudinal way to form identical daughter cells in the open water.

In the multiple fission type of reproduction, Euglena shows the stages of encystment where various daughter cells are reproduced longitudinally within the cyst.

Multiple Fission is usually performed under inactive conditions, that is when the favourable conditions of water, temperature, and food availability are not met. On the other hand, binary fission occurs in normal conditions.

While Binary fission means the formation of two daughter cells, Multiple fission means the formation of more than two daughter cells i.e. the production of multiple daughter cells.

READ MORE: How does Euglena reproduce? (Reproduction in Euglena)

Share This Post & Help Others!