In which one of the following protochordates notochord present only in the tail of larva?

Options

A. Ascidia
B. Balanoglossus
C. Myxine
D. Branchiostoma

Answer

To solve the question "In which one of the following protochordates is the notochord present only in the tail of the larva?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Question**:
- We need to identify which protochordate has a notochord that is present only in the tail of its larval stage.

2. **Analyzing the Options**:
- **Option A: Acedia**:
- Acedians (also known as ascidians or sea squirts) have larvae that possess a notochord only in the tail region. This is a defining characteristic of their larval form.
- **Conclusion**: This option is correct.

- **Option B: Balanoglossus**:
- Balanoglossus is a type of hemichordate, which has a notochord that extends beyond just the tail. It is not limited to the tail in its larval form.
- **Conclusion**: This option is incorrect.

- **Option C: Myxine**:
- Myxine, commonly known as hagfish, have a notochord that is present throughout their body, not just in the tail. This applies to both larvae and adults.
- **Conclusion**: This option is incorrect.

- **Option D: Phragmosoma**:
- Phragmosoma is another type of protochordate, but it does not have a notochord limited to the tail in its larval stage.
- **Conclusion**: This option is incorrect.

3. **Final Answer**:
- The only protochordate where the notochord is present only in the tail of the larva is **Option A: Acedia**.