Notochord is restricted to tail region in

Options

A. Hemichordata
B. Urochordata
C. Cephalochordata
D. Chordata

Answer

**Step-by-Step Solution:**

1. **Understanding the Notochord**: The notochord is a flexible rod-like structure found in the embryos of all chordates. It serves as a primary skeletal structure in some organisms and is a defining feature of the phylum Chordata.

2. **Identifying Organisms with Notochord in Tail Region**: The question specifically asks for organisms where the notochord is restricted to the tail region. This is characteristic of certain groups within the phylum Chordata.

3. **Recognizing Eurochordata (Tunicates)**: Eurochordata, also known as Tunicates, are a group of marine animals that exhibit this feature. In their larval stage, they possess a notochord that is confined to the tail region.

4. **Notochord in Adult Form**: It is important to note that in the adult form of Tunicates, the notochord is absent. This means that the notochord is only present during the larval stage and is restricted to the tail.

5. **Excluding Other Groups**:
- **Hemichordata**: In this group, the notochord is partial and not restricted to the tail.
- **Cephalochordata**: Here, the notochord extends from the head to the tail, not just confined to the tail.
- **Vertebrates (Caudates)**: In this group, the notochord persists throughout the body.

6. **Conclusion**: Based on the above analysis, the correct answer to the question is that the notochord is restricted to the tail region in Eurochordata (Tunicates).

**Final Answer**: The notochord is restricted to the tail region in Eurochordata (Tunicates).

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