Only the tail portion contains notochord in

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding the Notochord**: The notochord is a rod-like structure that provides support and is a characteristic feature of the phylum Chordata. It is present in various forms across different groups within this phylum.

2. **Identifying the Groups**: The question provides four options: Chordata, Cephalochordata, Hemichordata, and Urochordata. We need to analyze each group to determine where the notochord is located.

3. **Analyzing Chordata**: Chordata is a broad phylum that includes both protochordates (like Urochordata and Cephalochordata) and higher chordates (like mammals, birds, etc.). The notochord is present in some form in all chordates, but it is not limited to just the tail region.

4. **Analyzing Cephalochordata**: In Cephalochordata, the notochord extends along the entire length of the body, including the head region. Therefore, this option does not fit the criteria of having the notochord only in the tail.

5. **Analyzing Hemichordata**: Hemichordata is a separate phylum that does not have a true notochord. Instead, they have a structure called a stomochord, which is not equivalent to the notochord found in chordates. Thus, this option is also incorrect.

6. **Analyzing Urochordata**: In Urochordata (also known as tunicates), the notochord is present only in the tail region during the larval stage. In adult forms, the notochord is typically reduced or absent. This matches the question's criteria perfectly.

7. **Conclusion**: Based on the analysis, the correct answer to the question "Only the tail portion contains notochord in" is **Urochordata**.

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