12 julio, 2024

Choanoflagellates: what they are, characteristics, morphology, nutrition

What are choanoflagellates?

The choanoflagellates They are a group of organisms that belong to the protista kingdom and that have among their characteristics the presence of a flagellum that helps them move. This group of organisms is considered to be the closest, from the evolutionary point of view, to true animals.

There are two orders: Craspedida and Acanthoecida. The more than 150 that belong to this class are distributed between them. It is interesting to observe and study the similarities between the structure of choanoflagellates and choanocytes (sponge cells).

This group of organisms are of great interest to those who study the evolution of species, since from them it is possible to reconstruct the last unicellular ancestor of current animals.

Undoubtedly, choanoflagellates have been of great help in the various studies carried out on this subject.


The taxonomic classification of choanoflagellates is as follows:

Domain: eukarya
Kingdom: protista
Edge: Choanozoa
Class: choanoflagellatea


They have eukaryotic cells. This means that the genetic material (DNA and RNA) is enclosed in a structure very well delimited by a membrane, known as the cell nucleus.

– They are unicellular organisms, which means that they are made up of a single cell. This single cell presents a characteristic morphology, presenting a shape similar to an oval, sometimes being spherical.

– They have flagella, specifically a single flagellum, with a peduncle that serves to attach to the substrate. From the bottom of this peduncle arises the flagellum.

– Around the birth of the flagellum there is a kind of collar that surrounds it, made up of finger-shaped structures known as microvilli. These are filled with a protein known as actin.

– Inside the cell are certain organelles, such as food vacuoles and basal bodies.

– Sometimes the body of these organisms is covered by a layer known as the periplast. This is made up of proteins and, according to the type of organism, it can present a diverse composition, in addition to presenting distinctive characteristics such as scales, among others.

– The approximate diameter of the cells of the organisms that make up this class is 3-9 microns.

Characteristics of choanoflagellates

– Choanoflagellates are a group of organisms about which many aspects are still unknown. Regarding their lifestyle, the vast majority of the genera that make up this class are free-living.

– Some organisms that are closely related to this class have turned out to be parasites, so the description of species of parasitic choanoflagellates is not ruled out in the future.

– Many of the species are solitary, however, genera have been described whose species form simple colonies. Sometimes these colonies resemble clusters of grapes, in which each cell represents a grape and are attached to the same stem.

– These organisms can lead a sessile life or move in bodies of water. They can adhere to the substrate through a thin peduncle that they present.

– Those who move in the water do so thanks to the undulations of the only flagellum they possess. This movement of the flagellum develops water currents that give impetus to the choanoflagellate, facilitating its movement. This form of displacement allows them to be classified as opisthoconts, while most protists are called acroconts, since the flagellum they possess is located in front of them and in displacement it seems to «tow» them.


They are located mainly in aquatic environments. They are known to have a predilection for freshwater.

However, there are some species that also thrive in seawater. They live in this type of environment because that way they have access to their food source.


From a biological point of view, choanoflagellates are heterotrophic organisms. This means that they are not capable of synthesizing their own nutrients, so they must rely on other living beings to feed themselves, either from their own body or from organic substances manufactured by them.

Choanoflagellates feed mainly on organic particles found free in the water.

When they move through the water, as a result of the movement of the flagellum, detritus and bacteria are trapped in the microvilli around the flagellum, which constitute the main food of these organisms. They are later eaten.

Once inside the body of the choanoflagellate, the food particle is engulfed within the food vacuole, which contains a large number of digestive enzymes. These act on the food, fragmenting it into its constituent elements.

Once this occurs, the already fragmented nutrients are used by the cell in various processes, such as those that involve obtaining energy.

As a product of any digestive process, there are also remnants of substances that were not assimilated. These wastes are released into the extracellular environment.


Due to how simple these organisms are, they do not have specialized organs to carry out the uptake and transport of oxygen.

Taking this into account, respiratory gases (oxygen and carbon dioxide) cross the cell membrane through a process of passive cellular transport, diffusion.

Through this process, oxygen enters the cell, where there is little concentration of it, to be used in various metabolic processes.

At the end of these processes, carbon dioxide is obtained, which is released into the extracellular space, also by diffusion.


The type of reproduction of these organisms is asexual. This implies that the descendants will always be exactly the same as their parent. The process by which these living beings reproduce is called binary fission.

The first thing that must happen to start the process is the duplication of the DNA present in the cell nucleus. Once duplication has occurred, each copy of the genetic material is oriented toward each pole of the cell.

Immediately, the organism begins to divide longitudinally. Once the cytoplasm has undergone complete division, two daughter cells are obtained exactly the same as the one that divided.

It is important to mention that in choanoflagellates, this type of division is known as symmetrogenic. This means that the two daughter cells that are obtained are mirror images of each other, that is, one looks like the mirror of the other.

In these organisms the type of sexual reproduction has not been reliably established. It is believed that this type of reproduction occurs in some species, although this is still under study.


Bell, G. (1988) Sex and Death in Protozoa: The History of an Obsession. Cambridge: University Press.
Campbell, N. & Reece, J. (2007). Biology. Panamerican Medical Editorial. 7th edition.
Fairclough, S. & King, N. (2006). Choanoflagellates. Retrieved from: tolweb.org
King, N. (2005) Choanoflagellates. curr. Biol.

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