Paramecium – Classification, Structure & Function

The paramecium is a particular genus of unicellular ciliated protozoa. These particular protozoa are characterized by how they have literally thousands of cilia covering their form.

The paramecium is primarily found in brackish, marine, and fresh waters. Although you can also find them attached to the water surface too. They reproduce through asexual ways, using binary fission and are shaped something like a slipper, or shoe.

They exhibit conjugation as well. Paramecium are very simple to cultivate and are very often utilized to study a wide variety of biological structures and processes.

These organisms are so interesting and intriguing with such a wide application to science and otherwise, that we simply cannot resist writing about them, and if you have not yet been introduced, we are very happy to be the ones to introduce you to paramecium.

An Introduction To Paramecium


The shape of the paramecium somewhat resembles the bottom of a shoe, or a slipper. It is a unicellular organism, and can range in size from a measly 50um to a more significant 300um. However, this size does vary from paramecium to paramecium.

They are usually found in freshwater more than any other water types.

Paramecium is a single-celled eukaryote, and they belong to the Protista kingdom, and the ciliate protozoa genus.

They also belong to the phylum ciliphora as well!

Their bodies are covered in filaments that are small and look a little like tiny hairs, these are known as cilia, and they aid in locomotion.

They also have a very deep groove, this contains oral cilia, although this is not so clear to the eye.

Its oral cilia has the main job of aiding in locomotion, but it also grabs at food and pulls it into its oral cavity.

This is all deeply fascinating, so let’s move on to the classification of this organism.

Classifying Paramecium

Paramecium has many different characteristics, which means that it can be classified into phylum and sub-phylum based on these.

Let’s take a look at these classifications.

Phylum: Paramecium is a protozoa phylum.

Sub-Phylum: Paramecium is a ciliophora sub-phylum.

Class: Paramecium is the ciliates class.

Order: Paramecium is the hymenostomatida order.

Genus: Paramecium is in the paramecium genus.

Species: Paramecium is in the species caudatum.

Paramecium is a well-known and documented protozoan, it provides a higher level cellular differentiation as it contains a plethora of complicated organelles that undergo specific functions that allow its existence to be possible.

Despite it having a highly specialized composition, it also is complicated in how it reproduces as well. As there are 10 overall species of this particular organism, there are 2 that are the most common; these are P. caudatum, and P. aurelia.

Structure & Functionality

Structure & Functionality

Are you fascinated yet? You should be! It just gets more interesting from here! Classification can tell you how science defines paramecium, but if you are sitting there wondering what are paramecium then this is where you will really find out what you want to know.

So, let’s get down to the nitty-gritty information that truly defines paramecium.

Paramecium Size & Shape

The P.cadatum paramecium is microscopic in its size. It can range from 170um to 290, 300, or eve 350um! What is even more special about this organism? It is actually visible to the naked eye! No need for a microscope, or even a magnifier!

It is shaped like a shoe sole, or more like a slipper, hence why it is also given the nickname slipper animalcule.

Its posterior end is pointed and thick, it is a bit like a cone shape, however the anterior part of its body is more blunt, and broad. Its widest body part is just below its middle. Thus making the body asymmetrical.

Its oral surface is well-defined, and it has a convex aboral/ dorsal body.

Paramecium Pellicle

What about its pellicles? Well, its entire body is covered with these. They are thin, flexible, but firm membranes.

They are elastic naturally, supporting the cell’s membrane. These pellicles are made up of a substance that is gelatinous.

Paramecium Cilia

Its cilia are one of the most fascinating parts of this organism, so we will spend more time talking about this.

This is a reference to those multitudes of tiny hair-type projections that cover the paramecium’s body. These ‘hairs’ are spread along its body is longitudinal rows, they have uniformed legs as well.

This is known as being holotrichous. There are also a select amount of long cilia that you will find at the posterior end of the paramecium. This forms something of a caudal tuft, hence named a caudatum! (Makes sense now, right?)

The whole structure of these cilia is similar to flagella. Simply a sheath made of plasma membrane or protoplast, having longitudinal fibrils that form the shape of a ring.

These external fibrils are much thicker than the ones on the inside, each has a cilium that rises from a granule at the base.

Each of the cilia have a diameter of exactly 0.2um, and they aid in the locomotion of the animal.


Now, to fundamentally understand the structure of  the paramecium, we need to understand the parts that contribute to its form.

Let’s take a look at these parts in order.

The Oral Groove

The oral groove is a large, shallow, and oblique depression on the animal’s ventrio-lateral body side; this is called a peristome, or oral groove. It gives a somewhat asymmetrical appearance to this creature.

This then further extends into a depression, which is known as a vestibule, via a short cone-shaped funnel. It then expanded more into the cytostome through its opening, which is shaped much like an oval.

This is done via a long opening, this is known as a cytopharynx, then you have the esophagus, which leads to the vacuole for food.


The cytoplasm is a substance that is not unlike jelly. It is further differentiated into ectoplasm. This is basically just a peripheral, very narrow layer. It is actually rather dense, but translucent, it has an inner mass of semifluid plasmasol, or endoplasm which is shaped granular.


The cytopyge is found laying just behind the cytostome, on the ventral surface. It is also known as a cytoproct. All undigested food gets ejected through here.


The endoplasm is a more detailed part that makes up the cytoplasm. It contains in itself a plethora of granules. It also holds different structures and inclusions. This includes; nuclei, mitochondria, food vacuole, vacuoles, contractile vacuole, and so on.


Ectoplasm is a substance that creates a very dense, thin, and transparent layer that holds trichocysts, cilia, and fibrillar forms. It is bound onto the pellicle via a covering.


Trichocysts are something that you will find embedded into the cytoplasm. They have very small and spindly bodies. They are jam-packed with a dense refractive fluid that contains substances of which are swelled.

On these are cone-shaped heads at the spike of the outer end of their bodies. They are usually found to be perpendicular in relation to the ectoplasm of the paramecium.

The Nucleus

Remember when you studied biology in school, it is hard to forget about the nucleus, we all spent so much time learning about it. So, what do we know of the nucleus of the paramecium?

Well, the nucleus of the paramecium contained a micronucleus, and a macronucleus. Let’s look at this in a bit more depth.

The Micronucleus

The micronucleus is quite close in relation to the macronucleus. It is very small and has a tight structure. Its shape is like that of a sphere. It has fine chromatin threads and granules inside which are distributed evenly and uniformly throughout its cell, controlling cell reproduction.

The amount in a particular cell will vary depending on the species. For example there are no nucleolus found in caudatum.

The Macronucleus 

Ellipsoidal in shape, the macronucleus almost represents a kidney in its form. It is jam-packed with DNA. It controls all of its vegetative  functions, this is why it is also known as the vegetative nucleus.

Paramecium Vacuole

Much like how the paramecium has two nuclei, it also has two types of vacuoles as well. Let us look at these individually and understand them separately.

The Contractile Vacuole.

There are two of these contractile vacuoles on the dorsal side of the paramecium’s body. One is found at each end. These are full of fluids, and they will be found in places between the ectoplasm and the endoplasm.

It is not uncommon for them to actually disappear randomly, and this is why they are referred to as temporary organs.

Each of these has a connection to a bare minimum of five radical canals, and can be connected to a maximum of twelve.

Each radical canal will include a long ampulla, as well as an injector canal, and a terminal part. These will pour all the liquid from the whole body into the contractile vacuole, making it get bigger. It will then be released externally through an anal pore.

It is very irregular and unlikely for both contractile vacuoles to contract simultaneously. The posterior of these is found close in conjunction to the cytopharynx, thus it is likely to contract with greater speed, as there will be more liquid coming through.

There are three primary functions of a contractile vacuole, they include; excretion, respiration, and osmoregulation.

The Food Vacuole 

Then there is also the food vacuole. This does not contract, and in shape it appears more like a sphere. When found in the endoplasm, the size of this vacuole can vary. It will digest particles of food, as well as enzymes, and even small fluids and bacteria too!

These are the vacuoles associated with those granules which are digestive, and help the paramecium in digesting food.

Paramecium Characteristics

Paramecium Characteristics

If you want to go looking for the paramecium note that it is found worldwide and is free-living. You will usually find it in stagnant water pools, such as calm lakes, ponds, and even slow flowing water with abundant decaying organic compounds.

When you note how it moves, remember that the cilia help it to move, they actually allow the paramecium to travel at a speed of 4 times the length of its body every second. As it moves forward, it will rotate around itself, which helps it to take in more food.

Paramecium: A Conclusion

Aren’t these organisms unique? Everything about them is truly fascinating. Are you going to go looking in your local stagnant pools for them?

They are proof alone, that we have so much more to discover about our world.

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