Euglenoids are unicellular, microscopic organisms belonging to the Kingdom Protista. They are commonly found in freshwater bodies such as ponds and stagnant water, especially rich in organic matter. A well-known example of euglenoids is Euglena. They show characteristics of both plants and animals, making them unique organisms.
Characteristics of Euglenoid
Some characteristics of Euglenoid as Structure, Habitat, Habits, Reserve Food, and Reproduction are as follows:
- Euglenoids are more advanced than blue-green algae from an evolutionary point of view, for they have a definite, easily stained nucleus, and the chlorophyll is not scattered in granules but is localised in chloroplasts as in higher plants. The nuclear envelope persists during division.
- They are free-living and found in freshwater ponds and ditches or in damp soil.
- Euglenoids are distinguished by the absence of a cell wall, but they do contain flexible pellicles made up of protein.
- All the euglenoids have one or two flagella, by means of which they can swim easily.
- They bear a red-pigmented eye spot and a gullet near the base of the flagellum. The pigment in the eye spot is astaxanthin.
- Some euglenoids are green and holophytic (photoautotrophic) like other plants. Few are non-green and saprobic, like fungi and bacteria. Some capture and ingest the organisms like animals (holotropic).
- Photosynthetic forms bear many radiating chloroplasts. The chloroplasts contain pigments like chlorophyll a, chlorophyll b, and xanthophyll.
- Euglenoids reserve carbohydrates in the form of paramylum chemically distinct from starch and glycogen.
- Reproduction is usually asexual by cell division, but sexual reproduction has been reported in one genus.
- Under favourable conditions, euglenoids reproduce by simple, longitudinal binary fission.
- Examples: Euglena, Phacus, Peranema, Astasia, Trachelomonas.
Euglena - The Spindle Organism
Classification of Euglena
| Domain | Eukaryota |
|---|---|
| Kingdom | Protista |
| Superphylum | Discoba |
| Phylum | Euglenozoa |
| Class | Euglenoidea |
| Order | Euglenales |
| Family | Euglenaceae |
| Genus | Euglena |
Characteristics of Euglena
- Euglena is a large genus with 152 species.
- Euglena is a flagellated organism with no cell wall.
- In contrast to the lack of cell walls, which they resemble animals, euglenas usually have well-defined chloroplasts and store a carbohydrate only slightly different from the starches of higher plants.
- In the absence of sunlight and in the presence of organic matter, they ingest the food like other protozoans. That is why Euglena has been considered a plant by botanists and an animal by zoologists.
- The Euglena, when treated with antibiotic streptomycin or with heat, loses its chlorophyll; in other words, it can be converted from a plant to an animal.
- It needs special attention when one is searching for an organism that may represent the ancestral type from which plants and animals have evolved.
Euglena is studied as a plant as well as an animal. It is called a plant-animal.
Plant Characters of Euglena
- Presence of chloroplasts with chlorophyll.
- Holophytic (photosynthetic) nutrition.
Animal Characters of Euglena
- Presence of pellicle, which is composed of proteins and not of cellulose.
- Presence of stigma and paraflagellar body (photosensitive structures).
- Presence of a contractile vacuole (not found in plants).
- Presence of longitudinal binary fission.
Nutrition of Euglena
- Holozoic (animal-like), Holophytic (plant-like), and saprophytic nutrition can be seen in Euglena.
- Photoautotrophic nutrition.
- Euglena acquires its carbohydrate food by photosynthesis and nitrogenous food by absorption from the environment.
- Eugena is a mixotroph because it shows the saprotrophic and autotrophic modes of nutrition.
- Autotrophic, in the sense, means it makes its own food just like plants, and saprophytic, in the sense, means it feeds on other organisms to obtain carbon.
Locomotion of Euglena
- Flagella play a vital role in the movement of Euglena.
- It also shows euglenoid movement or metabolism, in which it betrays a slow worm-like movement by alternate contraction and expansion of the body.
- It shows phototaxis movement, i.e, responds to light or a stimulus of light.
Reproduction of Euglena
Euglena shows two types of reproduction, i.e, binary and multiple fission. No Sexual reproduction.
1. Binary Fission
- Euglena secretes a protective wall around itself and makes itself encysted under unfavourable conditions.
- After the encysted stage, two solitary daughters are formed when the organism splits longitudinally.
- The splitting starts from the former end and moves backwards. The nucleus elongates and divides into two.
- Finally, the individual is split into two, each half receiving one daughter nucleus.
2. Multiple Fission
- In the encysted stage, the nucleus splits often, and a huge number of minute daughter nuclei are generated.
- The cytoplasm smashes up, and a small amount surrounds each daughter nucleus, and various minute animals called flagellates are generated.
- Under favourable conditions, the flagellate comes out of the cyst and passes a short period through the amoeboid stage, develop into an adult Euglena.