Identifying euglena: under the microscope

If you see a marine or freshwater pool with algae growing in it, you are bound to find Euglena specimens there as well. Because euglenids are single-celled organisms, you cannot see them by just looking unless there are thousands or millions of them. To see individual specimens, you will need to view a single drop of water under a microscope.

With the naked eye

Euglenids are usually found wherever algae is growing because algae is one of the sources of food for this organism when it is feeding itself like an animal would. It has been placed in the Kingdom Protista along with parameciums and amoebas because many species of Euglena also photosynthesize like a plant. You would expect to find this microscopic protozoa closer to the surface and in water which is polluted with organic materials.

Several euglenids may be seen on the surface of brackish, saltwater or freshwater bodies or even neglected swimming pools as a soupy reddish- or greenish-colored slime. Warm temperatures form an especially favorable condition for euglenids to multiply by dividing themselves through the process known as mitosis.

Under the microscope

With over 150 species to the Euglena family, there are minor differences among species. Many of the euglenoid species are somewhat tear-drop shaped. The blunt portion of the body is the anterior ‘head’ of the organism; the more pointed part is the posterior section. Some pictures taken of Euglena specimens seem to show the posterior portion as being larger and more rounded. Other euglenoid species are ovoid in shape.

The only way to really tell the posterior from the anterior part of the body is where you locate the flagella. Euglenids have two flagella or whip-like structures located at the anterior end. The emergent flagellum tends to be longer than the other and is used to pull the organism through the water as it seeks out light or food. Sometimes the smaller of the two flagella may be seen but many times it is contained inside the Euglena in a reservoir. The flagella are usually best seen under a high-powered microscope.

Euglenids have no rigid cell wall to maintain a solid shape. The cytoplasm and organelles of the organism are held in by a plasma membrane. Under that and giving the outside ‘skin’ of the protozoa a ridged appearance is a pellicle. Viewed under a high power microscope, the pellicle has the contours of corrugated cardboard with crinkles and indentations. The raised portions of the pellicle are strips composed of protein and with a microtubule in each one. In some species of Euglena the strips extend the length of the organism’s body. In some euglenids, the pellicle ridges appear more like a corkscrew design. In Euglenas with that sort of strip placement, the organism can sometimes be seen wriggling through the water instead of using its flagella for locomotion. The wriggling movement is called metaboly.

In euglenids which photosynthesize, an eyespot or stigma may be seen in the anterior portion of the organism’s body. The eyespot appears red under the microscope and is used by the creature to sense where to move to get the most light. It is one of the most easily identifiable parts of a euglenid.

When you examine euglenids under the microscope, you will see a number of different-shaped spots throughout their bodies. These are the chloroplasts, paramylon bodies, contractile vacuoles and nucleus.

Not all euglenids are green. The ones that are have chloroplasts which contain chlorophyll a and sometimes chlorophyll b. Chlorophyll a is responsible for a green grass type of hue and is most responsible for photosynthesis. Sometimes a euglenid’s chloroplasts will contain chlorophyll b which is more of a bluish-green hue and increases the ability of the organism to absorb light by increasing the spectrum of light which can be utilized. Some euglenids which are colorless or reddish in color have carotenoids as pigments which display as yellow, orange or red. Chloroplasts can be just about any shape and size but are easy to see throughout the Euglena’s body.

The euglenids which have the added ability to ingest rotifers, paramecium or amoebas have gullets. This is used mainly when the euglenid is in darker conditions for prolonged periods of time and cannot photosynthesize.

You may also see several paramylon bodies, organelles which store starch-like carbohydrates in the form of a glucose compound produced through photosynthesis and used for reserve energy.

Contractile vacuoles in the euglenid’s body collect excess fluids and transfer them to the external environment. Without those organelles, the creature would grow too large for its plasma membrane and explode. These are found in freshwater euglenids.

The most important organelle in the euglenid’s body is the nucleus. It is a large circular structure found somewhere between the center to posterior of the organism. If your microscope is powerful enough, you may see one or more nucleoli or endosomes inside the nucleus and dot-like chromosomes sprinkled throughout the organelle. The nucleus regulates the activities of the euglenid and contains the DNA blueprint for reproduction.

Watch any video of the movement of a Euglena through the water and you will be captivated by this aquatic microorganism with the red eyespot.