The greatest ability of regeneration amongst the animals is found in

Options

A. Ascaris
B. Pheretima
C. Hirudinaria
D. Planaria

Answer

To solve the question regarding which animal has the greatest ability of regeneration, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Regeneration**: Regeneration is the biological process through which organisms can regrow certain parts of their body or even develop a whole new organism from a part of their body.

2. **Identifying the Options**: The options given are:
- A) Ascaris
- B) Perituma
- C) Eurydinaria
- D) Planaria

3. **Analyzing Each Option**:
- **Ascaris**: This is a nematode (roundworm) and does not have significant regenerative abilities. Therefore, it is not the correct answer.
- **Perituma**: This is a type of annelid (segmented worm) and also does not exhibit notable regenerative capabilities. Hence, it is not the correct answer.
- **Eurydinaria**: This is another annelid and similarly lacks significant regenerative abilities. Thus, it is not the correct answer.
- **Planaria**: This organism belongs to the phylum Platyhelminthes (flatworms) and is well-known for its remarkable regenerative abilities. Planaria can regenerate lost body parts and even form a complete organism from a small fragment of its body.

4. **Conclusion**: Based on the analysis, the organism with the greatest ability of regeneration among the options provided is **Planaria**.

### Final Answer:
The greatest ability of regeneration amongst the animals is found in **Planaria**.

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