Notochord is restricted to the tail region in

Options

A. hemichordata
B. urochordata
C. cephalochordata
D. vertebrata

Answer

To solve the question "Notochord is restricted to the tail region in," we will analyze each option provided and determine where the notochord is located in each group.

### Step-by-Step Solution:

1. **Understanding Notochord**:
- The notochord is a rod-like structure derived from the mesoderm that provides support to the embryo. It is a defining characteristic of the phylum Chordata.

2. **Analyzing the Options**:
- **Option 1: Hemichordata**:
- Hemichordates are not true chordates and do not possess a notochord. Instead, they have a structure called a stomochord, which does not serve the same function as a notochord. Therefore, this option is incorrect.

- **Option 2: Urochordata**:
- Urochordates (like tunicates) have a notochord that is present only in the larval stage, specifically in the tail region. In adult forms, the notochord is absent. This fits the question's criteria.

- **Option 3: Cephalochordata**:
- In cephalochordates (like lancelets), the notochord extends from the head to the tail throughout the organism's life. This means it is not restricted to the tail region, making this option incorrect.

- **Option 4: Vertebrata**:
- In vertebrates, the notochord is present during the embryonic stage but is replaced by the vertebral column in adults. It is not restricted to the tail region, thus this option is also incorrect.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option 2: Urochordata**, where the notochord is indeed restricted to the tail region during the larval stage.

### Final Answer:
**Urochordata**