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Stentor: A Trumpet-Shaped Organism With Interesting Behavior

Linda Crampton has an honors degree in biology. She has taught high school biology, chemistry, and physics as well as middle school science.

An Interesting Predator

Stentor is a single-celled organism that's shaped like a trumpet when it's extended. It's interesting to observe, especially when it's catching its prey. The organism has some impressive features. Researchers have discovered that Stentor roeselii seems to make relatively complex decisions with respect to avoiding harm. It can "change its mind" about its behavior as a dangerous stimulus continues. Understanding the biology of this process might help us understand the behavior of our cells.

Stentor is found in ponds and other bodies of still water. It's between one and two millimetres long and can be seen with the naked eye. A hand lens provides a better view. A microscope is required in order to see details of the organism's structure and behavior. If a microscope is available, watching a living Stentor can be a very absorbing activity.

Stentor Terminology

Stentor is referred to as a ciliate, a protist, or a protozoan. All of these terms are considered to be acceptable. The world of microscopic organisms is intriguing, whatever names are used to describe the creatures.


Stentor is a member of the phylum Ciliophora. The organisms in this phylum are commonly known as ciliates and live in aquatic environments. They are unicellular and bear hair-like structures called cilia on at least some part of their body. The cilia beat and move the surrounding fluid. In some organisms, they move the cell itself. Though ciliates are usually referred to as microorganisms and are studied by microbiologists, Stentor is visible without a microscope.


Stentor, other ciliates, and some additional organisms are sometimes referred to as protists. Protista is the name of a biological kingdom. It contains unicellular or unicellular-colonial organisms, including Stentor, as well as some multicellular ones The kingdom system is often used to classify organisms in schools. Scientists prefer to use the cladistic system of biological classification.


Ciliates and some other unicellular organisms are sometimes referred to as protozoa. This is an old term that comes from the Ancient Greek words proto (meaning first) and zoa (meaning animal).

The word "Stentor" is a genus name as well as a common name. Multiple species exist in the genus. S. coeruleus is named for the blue-green pigment called stentorin that it contains. S. roeselii was used in the recent experiment concerning the organism's "change of mind" behavior. S. polymorphus contains living algae.

Habitat and Structure of a Stentor

Stentor was named after a Greek herald in the Trojan War who is mentioned in Homer's Iliad. In the story, Stentor had a voice as loud as fifty men. The single-celled organism with the same name lives in bodies of fresh water. Its habitats include ponds, slow-moving streams, and lakes. It spends some of its time swimming through the water and the rest attached to submerged items such as algae and debris.

When it's swimming, Stentor has an oval or a pear shape. When it's attached to an item and feeding, it has a trumpet or horn shape. Its covered by short, hair-like cilia. The edge of the trumpet opening bears much longer cilia. These beat, creating a vortex that pulls in prey.

Stentor is attached to the substrate by a slightly expanded region known as the holdfast. It has the ability to contract into a ball when it's joined to a substrate. In some individuals, a covering called a lorica surrounds the holdfast end of the cell. The lorica is mucilaginous and contains debris and material excreted by the Stentor.

Stentor has organelles found in other ciliates. It contains two nuclei—a large macronucleus and a small micronucleus. The macronucleus looks like a beaded necklace. Vacuoles (sacs surrounded by membrane) form as needed. Ingested food enters a food vacuole, where enzymes digest it. Stentor also has a contractile vacuole, which absorbs water that enters the organism and expels it to the outer environment when it's full. The water is released through a temporary pore in the cell membrane.

Life of a Stentor

Stentor can stretch its body far beyond the substrate as it feeds. It eats bacteria, more advanced single-celled organisms, and rotifers. Rotifers are also interesting creatures. They are multicellular, but they are smaller than many unicellular ones and much smaller than a Stentor.

Stentor polymorphus and a few other species contain a single-celled green alga named Chlorella, which survives in the ciliate and performs photosynthesis. Stentor uses some of the food that the algal cells produce. The alga is protected inside the ciliate and absorbs substances that it needs from its host.

The Stentor species that have been studied reproduce primarily by splitting in half, a process known as binary fission. They also reproduce by attaching to one another and exchanging genetic material, which is known as conjugation.

The video below is interesting and well worth watching. As one of the creators says in a YouTube comment, however, the commentary contains an error. Tardigrades contain eight legs, not six.

The Genetic Code

Researchers are discovering that Stentor has multiple features of special interest. Three of these features are its genetic code, its ability to regenerate, and the polyploidy in its macronucleus.

Stentor primarily uses the standard genetic code, which we use. Other ciliates whose genome has been studied have a non-standard code. The genetic code determines many of an organism's characteristics. It's created by the order of specific chemicals in the nucleic acid (DNA and RNA) of a cell. The chemicals are called nitrogenous bases and are often represented by their initial letter.

Each sequence of three nitrogenous bases has a particular meaning, which is why the code is referred to as a triplet code. The sequence is known as a codon. Many codons contain instructions related to the manufacture of polypeptides, which are the chains of amino acids used to make protein molecules.

In the standard genetic code, UAA and UAG are called stop codons because they signal the end of a polypeptide. (U represents a nitrogenous base called uracil, A represents adenine, and G represents guanine.) Stop codons "tell" the cell to stop adding amino acids to the polypeptide that is being made and that the chain has been completed. UAA and UAG are stop codons in us and in Stentor coeruleus. In most ciliates, the codons tell the cell to add an amino acid called glutamine to the polypeptide that is being produced instead of signaling the end of the chain.

Even tiny fragments (of Stentor), 1/64th the size of the original cell, are able to regenerate into a small but normally proportioned cell, and then grow to the full size.

— Athena Lin et al, Journal of Visualized Experiments

Regeneration and Polyploidy

Stentor is known for its amazing ability to regenerate. If its body is cut into many small pieces (anywhere from 64 to 100 segments, according to different sources), each piece can produce an entire Stentor. The piece must contain a portion of the macronucleus and the cell membrane in order to regenerate. This is not as unlikely a condition as it may sound. The macronucleus extends through the whole length of the cell, and a membrane covers the entire cell.

The macronucleus exhibits polyploidy. The term “ploidy” means the number of sets of chromosomes in a cell. Human cells are diploid because they have two sets. Each of our chromosomes contains a partner bearing genes for the same characteristics. The Stentor macronucleus contains so many copies of chromosomes or segments of chromosomes (tens of thousands or higher, according to various researchers) that it's highly likely that a small piece will contain the necessary genetic information to create a new individual.

Scientists have also observed that a Stentor has an amazing ability to repair damage to the cell membrane. The organism survives wounds that would most likely kill other ciliates and single-celled organisms. The cell membrane is often repaired and life appears to go on as normal for an injured Stentor, even when it has lost some of its internal contents through a wound.

Changing a Response to a Stimulus

Stentor consists of just one cell, so many people likely have the impression that its behavior must be very simple. There are two problems with this assumption. One is that researchers are discovering that the activity in cells—including our own—is far from simple. The second is that scientists at the Harvard Medical School have discovered that at least one species of Stentor can change its behavior based on the circumstances.

The Harvard research was based on an experiment performed in 1906 by a scientist named Herbert Spencer Jennings. Stentor roeselii was (supposedly) the subject in his experiment. Jennings added carmine powder to the water by the trumpet shaped openings of the ciliate. Carmine is a red dye. The powder was an irritant.

The scientist noticed that at first Stentor bent its body to avoid the powder. If the powder kept on appearing, the ciliate reversed the direction of its cilia movement, which would normally have pushed the powder away from its body. If this action didn't work, it contracted its body into its holdfast. If this failed to protect it from the irritant, it detached its body from the substrate and swum away.

The results of the experiment attracted the attention of other scientists. A 1967 attempt to repeat the experiment couldn't replicate the discoveries, however. Jennings' work was discredited and ignored. Recently, a Harvard scientist became interested in the experiment and by the fact that its results were refuted. After investigating the situation, he found that the 1967 experiment had used Stentor coeruleus, not Stentor roeselii, because the researchers couldn't find the latter species. The two species have slightly different behavior.

The Harvard researchers tried using carmine powder as an irritant for S. roeselii but didn't see much response. They discovered that microplastic beads were an irritant, however. They were able to replicate all of Jennings' observations by using the beads. They also made some new discoveries.

They do the simple things first, but if you keep stimulating, they 'decide' to try something else. S. roeselii has no brain, but there seems to be some mechanism that, in effect, lets it 'change its mind' once it feels like the irritation has gone on too long.

— Jeremy Gunawardena, Harvard Medical School

Fascinating Behavior in a Single-Celled Animal

The Harvard researchers found that some individuals had a slightly different set of behaviors from others and in a few an orderly sequence wasn't observed, but in general a clear sequence of behaviors was observed in response to the continuous presence of the irritation.

Most of the time, the individual Stentors first bent away from the stimulus and reversed the direction of their cilia. These behaviors were often performed simultaneously. As the irritation continued, the Stentors contracted and then in some cases detached from the substrate and swam away.

It might be wondered why scientists at a medical school are interested in the behavior of a ciliate. They believe that the behavior shown by Stentor might apply to the development of a human embryo, the behavior of our immune system, and even cancer.

No scientist is suggesting that Stentor has a mind, despite the use of the phrase "change its mind". Nevertheless, the discovery of its reaction to a harmful stimulus and its more autonomous behavior compared to that of other cells could be important with respect to our biology. As the researchers in the second referenced article below say, Stentor challenges our assumptions about what a cell can or cannot do.

Stentor coeruleus and its macronucleus

Stentor coeruleus and its macronucleus

Potential Benefits of Studying Stentor

Stentor hasn't been as well studied as other ciliates, though this may be about to change. Until recently, researchers were unable to create a large population of the organism in captivity, even by binary fission. The ciliate also has a low mating frequency, at least under captive conditions. The situation seems to be improving as scientists are becoming interested in Stentor and are learning more about its behavior and requirements for survival.

The researchers who are studying the organism have discovered some intriguing facts, but there are still many unanswered questions about its life. It will be very interesting to discover whether any of our cells behave in ways similar to Stentor. Studying the nature and behavior of its cell may teach us more about the ciliate and perhaps more about our cells as well.


  • Ciliata morphology from UCMP (University of California Museum of Paleontology)
  • Stentor coeruleus information from Current Biology
  • The study of regeneration in Stentor from Journal of Visualized Experiments/US National Library of Medicine
  • The macronuclear genome in Stentor coeruleus from Current Biology
  • Complex decision making in a single-cell organism from the ScienceDaily news service

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on June 22, 2020:

Thanks, Umesh. I appreciate your visit.

Umesh Chandra Bhatt from Kharghar, Navi Mumbai, India on June 22, 2020:

Amazing article. Unique topic. New information for me.

Linda Crampton (author) from British Columbia, Canada on March 30, 2020:

As I say in the article, Stentor reproduces primarily by binary fission but also exhibits conjugation. Binary fission is a type of asexual reproduction and conjugation is a type of sexual reproduction. I describe the importance of Stentor’s macronucleus in the article. In general, the macronucleus of a ciliate controls development and metabolism and the micronucleus becomes active during reproduction.

aidan fredette on March 26, 2020:

Is the stentor A-sexual or reproduce sexually? Also what's the point of the macro and micro-nucleus

Linda Crampton (author) from British Columbia, Canada on February 03, 2020:

The trumpet shape is interesting. I hope researchers soon discover more about Stentor and its life.

Suchismita Pradhan from India on February 03, 2020:

I never knew about this organism before reading your article.Thanks for introducing me.Iam more fascinated towards trumpet like structure.I know amoeba but stentar is new to me.

Linda Crampton (author) from British Columbia, Canada on February 03, 2020:

Thanks for the visit, DreamerMeg. A microscope is a wonderful instrument because it can reveal so many unexpected things. I think that Stentor is the most interesting member of the group that you've mentioned as well, though I enjoy observing the others.

DreamerMeg from Northern Ireland on February 03, 2020:

I used to love watching the organisms in pond water under a microscope. As you say, they are fascinating. I do not recall hearing about Stentor before, even more fascinating than amoeba, euglena and paramecium!

Linda Crampton (author) from British Columbia, Canada on January 26, 2020:

Hi, Peggy. I think the microscope is a wonderful instrument. It's amazing what can be seen with it, as you say. Thanks for the visit.

Peggy Woods from Houston, Texas on January 26, 2020:

It is amazing what can be seen with the help of a microscope. Thanks for introducing me and others to the fascinating world of stentors. That first video where the stentor was injured and then went on to heal itself was interesting to view. Perhaps with more study, scientists will discover things about stentors that can aid humans when injured or facing things like cancer. Thanks, Linda, for writing about this.

Linda Crampton (author) from British Columbia, Canada on January 24, 2020:

Thanks for the visit, Linda. I think they're amazing organisms, too.

Linda Chechar from Arizona on January 24, 2020:

These are amazing organisms. They are incredibly microscopic trumpet shapes.

Linda Crampton (author) from British Columbia, Canada on January 13, 2020:

Thanks, Eman. Tiny organisms are interesting to investigate.

Eman Abdallah Kamel from Egypt on January 13, 2020:

A very interesting article. It is the first time I read about the Stentor organism.

Linda Crampton (author) from British Columbia, Canada on January 11, 2020:

Hi, Nithya. I'm looking forward to new discoveries about Stentor. I suspect that it may have more to teach us.

Nithya Venkat from Dubai on January 11, 2020:

An interesting and informative article about the Stentor. It is amazing how such a simple organism can be a source of detailed research that can lead to discoveries that help human beings.

Linda Crampton (author) from British Columbia, Canada on January 11, 2020:

Thanks for raising the interesting points, Mel. I appreciate your comment.

Mel Carriere from Snowbound and down in Northern Colorado on January 11, 2020:

What is a "mind" anyway, but a sophisticated bundle of neurons? I think the Stentor's behavior indicates that we multi-celluar beings, despite our illusions of grandeur, are really not all that special. Thanks for once again teaching me something I didn't know.

Linda Crampton (author) from British Columbia, Canada on January 10, 2020:

Thank you very much, Liz. I think the natural world is amazing, too!

Liz Westwood from UK on January 10, 2020:

This is a fascinating account. It highlights how amazing the natural world is and draws attention to a tiny organism that we could easily overlook.

Linda Crampton (author) from British Columbia, Canada on January 09, 2020:

Hi, Liza. I think it's an exciting topic, too. A microscope can reveal a new and surprising world! Thank you for the comment.

Liza from USA on January 09, 2020:

This article is such an exciting topic, Linda. I think the last time I used the microscope when I was in a biology class in high school. I bet it was fascinating to see this organism under the microscope. Thank you for sharing this experimental article, Linda.

Linda Crampton (author) from British Columbia, Canada on January 08, 2020:

Hi, Dora. I find all cells fascinating, but I must admit that I find Stentor's behaviour amazing. Thank you very much for the visit.

Dora Weithers from The Caribbean on January 08, 2020:

The regenerative ability of the stentor is most intriguing. The ability to "change its mind" is mind-boggling. Thanks for this interesting lesson on another creature I would not have heard of, if it weren't for your science lessons.

Linda Crampton (author) from British Columbia, Canada on January 08, 2020:

Hi, Nell. I think the microscopic world is very interesting. There always seems to be something new to learn about the organisms there.

Nell Rose from England on January 08, 2020:

How fascinating. I have never heard of Stentors before. I am always amazed at these shapes, and how they are named. Interesting stuff, thanks

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Hi, Denise. I think all of the ciliates are interesting. Watching them under a microscope can be fascinating!

Blessings to you.

Denise McGill from Fresno CA on January 07, 2020:

How informative. I've been introduced to paramecium but never heard of stentors before.



Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Thank you for such a lovely comment, Donna. I appreciate your kindness very much!

Donna Rayne from Sparks, NV on January 07, 2020:

Linda, I wish there were "like" buttons so that I can "like" what people are saying to you!

You are an awesome writer my friend :)

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Thanks for the comment, Heidi. I hope you have a great 2020!

Heidi Thorne from Chicago Area on January 07, 2020:

Leave it to you to show us, again, the world around us that we can't see. Keep the interesting stuff coming in 2020. Happy New Year!

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Hi, Flourish. It is a surprising organism. It seems to have developed some advanced and impressive features over time. It will interesting to see if any of our cells have features that resemble those of Stentor.

FlourishAnyway from USA on January 07, 2020:

This is pretty wild, Linda. I was impressed at the regeneration when you cut it into 64-100 little pieces but then with the irritant description it does to have a little “mind.”

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Thanks, Penny. I think that Stentor is a fascinating organism.

Penny Leigh Sebring from Fort Collins on January 07, 2020:

Fascinating, particularly the more exaggerated reactions to stimuli! Thank you for an interesting read!

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Thank you for raising some interesting points, Manatita. The nature of existence is fascinating to consider. I appreciate your visit.

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Hi, Pamela. I suspect that scientists may do more research about the ciliate soon. I hope they do. It may have some additional features that might help us.

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Hi, Bill. Stentors are interesting to observe. I've seen them as well and enjoy watching them. I appreciate your comment, as always. I hope you have a good week.

Linda Crampton (author) from British Columbia, Canada on January 07, 2020:

Thanks, Devika. I appreciate your comment very much.

Devika Primić from Dubrovnik, Croatia on January 07, 2020:

Amazing facts of an unusual cells. I find this hub fascinating and informative. In detail and you know how to share a well researched hub on different titles. Your work amazes me and surprises me too.

Bill Holland from Olympia, WA on January 07, 2020:

I have actually seen them. I finally had some firsthand knowledge of what you were talking about. lol You know I always love your articles. Keep them coming please.

Pamela Oglesby from Sunny Florida on January 07, 2020:

Rhw stentor is amazing! I have never heard of the stentor until now, and it was fascinating to watch in the videos. Thanks for all the great information and it does sound like scientist will be doing a lot more research on the stentor.

manatita44 from london on January 07, 2020:

One of your deeper, richer, more studious ones. They do not have minds, no, but they have souls like all sentient and non-sentient beings, are driven to behave in a particular way by 'Higher forces'.

Yes, it will be nice to know more but life is in motion and I'm sure we will, sooner or later.

The videos are attractive and do bring them to life.

Linda Crampton (author) from British Columbia, Canada on January 06, 2020:

Thank you very much for the visit and for such a kind comment. Donna!

Donna Rayne from Sparks, NV on January 06, 2020:

Wow! Fascinating and captivating to say the least. You did a great work in your studies and in teaching us the mystical part of cells that we don't even know about and leaves me to wonder how our cells work together just as beautifully as the Stentor!

Great work!

Donna Rayne