1.hydra-budding2.euglena-longitudinal binary fission 3.planaria-regenration4.paramecium-transverse binary fission

Longitudinal Binary Fission in Animals

Introduction:
Binary fission is a form of asexual reproduction in which a single organism divides into two daughter organisms. It is a common mode of reproduction in many unicellular organisms, but it is also observed in certain multicellular animals. Among the given options, the animal that undergoes longitudinal binary fission is Planaria (option 3).

Planaria:
Planaria is a type of flatworm that belongs to the class Turbellaria. It is known for its remarkable regenerative abilities and ability to reproduce through longitudinal binary fission.

Process of Longitudinal Binary Fission in Planaria:
The process of longitudinal binary fission in Planaria can be explained as follows:

1. Initiation:
A mature Planaria individual starts the process of binary fission by undergoing longitudinal division. The process begins with the formation of a transverse groove near the middle of the body.

2. Division:
As the groove deepens, the Planaria's body starts to split into two halves along the longitudinal axis. This division occurs gradually, starting from the posterior end and extending towards the anterior end.

3. Regeneration:
During the division process, each half of the Planaria's body starts regenerating the missing parts. This regeneration is possible due to the presence of pluripotent stem cells called neoblasts, which are capable of differentiating into various cell types.

4. Separation:
Once the division is complete and regeneration has occurred, two separate and fully functional Planaria individuals are formed. Each individual then continues to grow and regenerate independently.

Advantages of Longitudinal Binary Fission:
1. Efficient Reproduction: Longitudinal binary fission allows Planaria to reproduce rapidly, resulting in the population expansion of these organisms.

2. Genetic Diversity: Although binary fission is an asexual mode of reproduction, genetic diversity can be achieved through mutations and genetic variations during the regeneration process.

3. Regenerative Abilities: Planaria's ability to regenerate missing body parts during binary fission is advantageous in terms of survival and adaptation to changing environments.

Conclusion:
In conclusion, among the given options, Planaria is the animal that undergoes longitudinal binary fission. This unique method of reproduction allows Planaria to efficiently reproduce, regenerate missing body parts, and adapt to different environmental conditions.