Euglena is a single-celled organism that combines characteristics of both plants and animals. This microorganism uses sunlight to produce its own food, similar to plants, yet it can also move freely and consume other particles, much like an animal. Its distinctive physical attributes and dynamic movements contribute to its notable appearance.
General Shape and Dimensions
Euglena exhibits an elongated form, often spindle-shaped or tear-drop shaped, with one end being somewhat rounded and the other tapering to a point. This microscopic organism is bright green, a color derived from its chloroplasts. However, some species might appear reddish due to the presence of carotenoid pigments.
The size of Euglena varies depending on the species, but most fall within a range of 15 to 500 micrometers in length. For instance, Euglena gracilis, a commonly studied species, measures between 31 and 70 micrometers long and 6 to 22 micrometers wide. Its minute size means that Euglena is far too small to be seen with the naked eye, requiring a microscope for observation. Under magnification, its characteristic outline becomes clearly visible.
Distinctive External Features
Euglena possesses several identifiable external structures. A prominent feature is the flagellum, a long, whip-like appendage that extends from the anterior, or front, end of the organism. While Euglena has two flagella, usually only one long one protrudes visibly from the cell. This flagellum appears as a slender filament, often seen waving or propelling the organism.
Near the anterior end, a small, reddish spot known as the eyespot or stigma is noticeable. This eyespot is composed of carotenoid pigments and functions by filtering light before it reaches a light-detecting structure at the base of the flagellum, rather than directly perceiving images. The outer surface of Euglena is covered by a flexible outer layer called the pellicle, which replaces the rigid cell wall found in plants. This pellicle is made of proteinaceous strips that give the surface a faintly striated or corrugated appearance under a microscope. Internally, numerous chloroplasts are visible as green, disc-shaped or elongated bodies.
Movement and Shape Changes
Euglena’s appearance is dynamic, changing as it moves through its environment. One primary mode of locomotion involves the flagellum, which beats or twists like a tiny propeller. This action pulls the organism forward through water, often resulting in a noticeable rotating motion of the entire cell.
In addition to flagellar movement, Euglena can change its body shape through euglenoid movement, or metaboly. The flexible pellicle allows the organism to contract and expand, enabling it to squeeze through tight spaces or inch along surfaces. During this movement, the Euglena’s elongated form can visibly shorten and widen, then narrow and extend again, creating a distinct undulating or “inchworm-like” progression.