The most primitive bilaterally symmetrical organism is :-

Options

A. Ascaris
B. Fasciola
C. Leucosolenia
D. Hydra

Answer

To determine the most primitive bilaterally symmetrical organism from the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Bilateral Symmetry**:
- Bilateral symmetry refers to organisms that can be divided into two identical halves along a single plane. This is a key characteristic of many animal phyla.

2. **Examine the Options**:
- The options provided are:
1. S-carriers (roundworms)
2. Feshula
3. Lugosolenia
4. Hydra

3. **Evaluate Each Option**:
- **S-carriers (Roundworms)**: These organisms exhibit bilateral symmetry, but they are not considered the most primitive.
- **Feshula**: This organism is known to be bilaterally symmetrical and is considered primitive among bilaterally symmetrical organisms.
- **Lugosolenia**: This organism is characterized by radial symmetry, not bilateral symmetry.
- **Hydra**: Like Lugosolenia, Hydra also exhibits radial symmetry.

4. **Identify the Correct Answer**:
- After evaluating all options, the only organism that is both bilaterally symmetrical and primitive is **Feshula**.

5. **Conclusion**:
- Therefore, the most primitive bilaterally symmetrical organism is **Feshula**.

### Final Answer:
**Feshula**

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