Identify the correct statement.

Options

A. All vertebrates are chordates but all chordates are not vertebrates.
B. All craniates are vertebrates but all vertebrates are not craniates.
C. All flatworms possess metamerism but all metamerically segmented organisms are not flatworms
D. All are correct.

Answer

To solve the question, "Identify the correct statement," we will analyze each statement provided in the options.

### Step-by-Step Solution:

1. **Analyze Statement A:**
- Statement: "All vertebrates are chordates but all chordates are not vertebrates."
- Explanation: Vertebrates are a sub-group of chordates. All vertebrates possess a notochord at some stage in their life cycle, which is a characteristic of chordates. However, there are chordates (like cephalochordates and urochordates) that do not fall under the vertebrate category. Therefore, this statement is **correct**.

2. **Analyze Statement B:**
- Statement: "All craniates are vertebrates but all vertebrates are not craniates."
- Explanation: Craniates include all vertebrates and also hagfish, which have a cranium but lack a vertebral column. Thus, while all vertebrates are craniates, not all craniates are vertebrates (since hagfish are craniates but not vertebrates). Therefore, this statement is **incorrect**.

3. **Analyze Statement C:**
- Statement: "All flatworms possess metamerism but all metamerically segmented organisms are not flatworms."
- Explanation: Flatworms (phylum Platyhelminthes) do not exhibit metamerism; metamerism is a characteristic of annelids (segmented worms). Therefore, this statement is **incorrect**.

4. **Conclusion:**
- Since Statement A is the only correct statement, the answer to the question is **Option A**.

### Final Answer:
The correct statement is **A. All vertebrates are chordates but all chordates are not vertebrates.**

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