Regeneration in Planaria


Planarians are able in creating new individuals from their body parts. This process is popularly known as regeneration and the factor shows that when the planarians are cut into several parts, each part gets the form of a new organism. The process differs from that of reproduction as regeneration can happen from any part of the organism. An example of this factor is that the tail of a lizard is cut down but after some time a new tail is formed.

What is Regeneration?

Regeneration is considered the process of development of a complete organism from the different parts of the body of the organism. In this case, regeneration happens of the damaged cells or if any parts are cut during an injury. Some organisms like starfish, hydra, and planaria are examples of this factor.

The part regeneration of planarian is most important here. It is said that they have the ability to give rise to new individuals from their body parts. It shows that after the process of regeneration, the compilations of organisms happened.

The Concept of Planarians

Planarians are mostly free-living flatworms. It belongs to the class of Turbellaria and it lies under the phylum Platyhelminthes. In this part, the term planaria is mainly described as the name designated to one genus. This name is mainly used for the description of any member of the family Planariidae.

Figure 1: Planarian

This kind of flatworms consist of eyes and it looks like a cross and the factor gives a cartoonish appearance. They consist of a three-branched intestine and a tubular pharynx. Here the location of the tubular pharynx is halfway down the body. It is seen that most of the phylum are parasites in nature.

They are also not harmful to humans and bear the characteristics of a soft, flat, and wedge-shaped body. The colour of the worms may be blue, brown, black, white, or grey. They have a blunt head which is triangular in shape and it is made up of two ocelli. The areas that are pigmented are seen to be very sensitive when coming into light.

Information regarding Planarian Regeneration

Research about the planarians says that they are the kind of very interesting animals. They are called so because they can regenerate their lost body parts.

Figure 2: Planarian’s Regeneration

While other animals in the same condition can die, planarians are able to regenerate. An example of this factor is that if the planarians are cut down to the middle they can regenerate into two separate individuals. The most important part here is that if they are cut into different pieces then each piece will form a new planarian. This feature of regeneration makes them immortal under the edge of a knife. Here, the new tissues can grow due to pluripotent stem cells.

The cutting of the head of this organism can make two new regenerated cells and thus they continue to live. The reproduction process of this organism is different and they reproduce through the fusion of gametes and it forms zygote and it is developed into a new organism.

Figure 3: Anatomy of a Planarian

They consist of a very simple system of organs and the digestive system consists of a mouth, pharynx, and a gastrovascular cavity. The location of the cavity is seen in the centre of the underside of the body. It bears the system of external digestion and the digestive enzymes are secreted from the mouth of the organism.

Key to Regeneration

Take the case of Schmidtea mediterranea, a kind of planarian. It consists of stem cells called neoblasts. In the process of regeneration, neoblasts are most important and here regeneration of missing tissues happens. In the case of adult animals, neoblasts are the only dividing cells. This can be compared to the stem cells of humans although they do not remain after the growth of the new cells.


This tutorial shows that the regeneration of planaria is an essential aspect. The development of a complete organism from different body parts is called regeneration. Some organisms like starfish, hydra, and planaria follow this process. It is also seen that planaria have the ability to give rise to new individuals. This process of regeneration can take place from any part of the body. They have specific sizes, colours, and shapes. They are seen to be tiny as well as complex in nature. They have different organs and reproduction as well as excretory organs.


Q1. Which factors can affect the process of regeneration of planaria?

Ans. It is seen that several factors affect the process of regeneration of planaria. The factors include chemical, temperature as well as seasonal factors. Here flatworms are applied as a classic model of the process of regeneration. The stem cell biology helps in gaining information on this factor.

Q2. What are the main differences between regeneration in planaria and hydra?

Ans. It is seen that planaria, as well as hydra, are able in the process of regeneration. The main difference is that hydra is capable of budding but planaria are not capable of budding. Hydra develops from the bottom of the part whereas planaria can form a complete organism wherever it is cut.

Q3. How long time does it take for planaria and hydra to regenerate?

Ans. Both planaria and hydra are capable of regeneration and it is seen that they take a different amount of time for this process. Planaria takes 2 weeks whereas hydra takes 3 days for this process.

Updated on: 13-Apr-2023


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