In some chordates, the notochord is modified as the vertebral column. Such animals are called vertebrates. Which one of the following statements makes sense?

Options

A. It is present only in larval tail in ascidian
B. All vertebrates are chordates but all chordates are all chordates are vertebrates.
C. All vertebrates are chordates but all chordates are not vertebrates.
D. Chordates are not vertebrates and vertebrates are not chordates.

Explanation

To solve the question regarding the modification of the notochord in chordates and the classification of vertebrates, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Notochord**: The notochord is a flexible rod-like structure found in chordates. It provides support and is a key feature in the development of the vertebral column in vertebrates.

2. **Identify the Subphyla of Chordates**: Chordates are divided into three main subphyla:
- Urochordata (e.g., ascidians)
- Cephalochordata (e.g., lancelets)
- Vertebrata (vertebrates)

3. **Analyze the First Option**: The first statement claims that the notochord is present only in the larval tail in ascidians (urochordates). This is correct because in urochordates, the notochord is indeed present only during the larval stage.

4. **Analyze the Second Option**: The second statement suggests that all vertebrates are chordates, but not all chordates are vertebrates. This is also true, as vertebrates are a subset of chordates.

5. **Analyze the Third Option**: The third statement indicates that vertebrates have a notochord during embryonic development, which is replaced by a vertebral column. This is accurate since vertebrates initially possess a notochord that is later replaced by either cartilage or bone.

6. **Analyze the Fourth Option**: The fourth statement claims that vertebrates are not chordates and vice versa. This is incorrect, as vertebrates are indeed a type of chordate.

7. **Conclusion**: Based on the analysis, the correct statements are:
- Option 1: Correct
- Option 2: Incorrect
- Option 3: Correct
- Option 4: Incorrect

Thus, the statements that make sense are options 1 and 3.

### Final Answer:
The correct statements are:
- Option 1: It is present only in larval tail in ascidian.
- Option 3: All vertebrates are chordates, but not all chordates are vertebrates.