Is the Euglena Plant or Animal?

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Euglena plant or animal?
Euglena Plant or Animal? – NOAA

Is the Euglena  plant or animal? Or is it something else? The year is 2019. I am seventy-one. Yet I recall my school days and my sophomore year high school biology. One day the teacher, Miss Warne, discussed a single cell creature with her class. It has a whip like thread called a flagellum. That creature is the euglena.

The flagellum pulls rather than pushes the euglena through the water.  Such locomotion is at least suggestive that euglena is an animal. Yet, the euglena has chloroplasts like a plant.

Euglena Plant or Animal?

While it has chloroplasts like a plant, the euglena lacks another characteristic of plants, a cellulose wall. It feeds in animal fashion, but it also produces sugar like a plant does. It has a light-sensitive area called an eyespot. Because it resembles both animals and plants, scientists have resisted categorizing euglena as either one. Was a final decision made? Well yes there was. What decision do you think they made?

The Decision: Don’t Decide

Nearly sixty years later has modern science confidently relegated the euglena to an appropriate place in the scheme of things? A “no” answer might seem the coward’s way out. Yet scientists have conveniently added another kingdom.

The new kingdom classification is Protista. Other single celled organisms have been assigned to that kingdom. Among them are the ameba and the paramecium. In the opinion of this scientist, there are only two valid kingdoms to choose from, the animal kingdom and the plant kingdom. Of the two, the choice should be: euglena is an animal.

One final thing: even if assignment to another kingdom possesses validity, even if… Is there reason to say a member of that kingdom can change kingdoms, say to become a plant or an animal?

Note: You might also enjoy Are They Alive? DNA, Viruses, Gametes


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14 thoughts on “Is the Euglena Plant or Animal?

  • Thank you for your approved comment, Anika. There’s my point, really. The “scientists” could not determine if it is animal or plant. They copped out by inventing another category.

  • The euglena is neither a plant nor an animal [because] in the absence of sunlight it kills and eats its victims by wrapping around them, spraying them with gastric juice and sucking them up, and a euglena, in the presence of sunlight, uses its chloroplast to manufacture food.

  • Hi Vince, I stumbled across your very enjoyable blog while searching for something else. I thought I’d clarify a couple of things about Euglena and their place among other eukaryotes.

    Phylogeny puts the animals and euglenoids very far apart in the eukaryote tree of life. The animals (metazoa) are a distinct monophyletic lineage within the group Opisthokonta. We animals are closely related to the choanoflagellates, which are morphologically very similar to choanocyte cells on sponges; and we are more distantly related to the fungi (which are also opisthokonts), and still more distantly related to the Amoebozoa. What that means is that the common ancestor we share with all those groups lived more recently than our common ancestor with Euglena.

    The Euglenozoa fall within a segment of the tree that branched out earlier, the Excavata. This group contains a large diversity of flagellated organisms, including such well-known troublemakers as Giardia and Trichomonas.

    The plants are on yet another branch, a multicellular group within Archaeplastida, which also contains the green and red algae. The Archaeplastida are descended from an ancestral organism that had acquired the ability to photosynthesize by forming a symbiotic relationship with a cyanobacterium (chloroplasts are remnants of an earlier symbiosis with a photosynthetic bacterium).

    Now, here’s the curious thing: at some point in the distant past, certain Excavata in the branch we call Euglenozoa acquired chloroplasts of their own by forming a symbiotic relationship with a green alga (from the Archaeplastida, the group that contains plants). This “secondary symbiosis” resulted in a separate lineage of photosynthetic flagellates. Some groups within that lineage later lost their chloroplasts, but Euglena retain them.

    So, while Euglena are neither plants nor animals, they do possess organelles formed from ancient symbionts that were green algae, which are viridiplantae (true plants, in the loose sense). Genes from these symbionts have been incorporated into the genomes of the photosynthesizing euglenoids. Consequently, one could argue that Euglena are at least partly “plants”, by virtue of secondary symbiosis. However, they do not fall within Plantae, which is a very restricted group of archaeplastids.

    For a good overview of various eukaryote lineages, see:

    • Bruce, I kept your comment, as it was spoken intelligently and respectfully. To be honest with you, to me? I view this as pseudoscience. Not legitimate science. But others will likely disagree. They have a right to express their perspective, their “take.”

  • Ajab

    I think it is both because it has chloroplasts like a plant. It feeds in animal fashion, but it also produces sugar like a plant does.

  • Could they have invented the term protist to indicate first forms of life? If so, then they’re pushing evolution as a fact. Hulloo! It’s nothing more than a theory and a rather poor one at that.

  • Human Beings have a tendency to categorize things. We like classifications, it simplifies things for us. Just because some things seem to fit neatly into classifications we can devise, does not mean that all things will do so.

  • Destiny Mathis

    Early scientists were confused by euglena because they wanted to classify all organisms as either plants or animals so they created a new group of organisms and put euglena in this group.

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