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 of identifying the correct statement, let's analyze each statement step by step.

### Step 1: Analyze Statement 1
**Statement:** All vertebrates are chordates, but all chordates are not vertebrates.

**Explanation:**
- Chordates are a phylum that includes all animals with a notochord at some stage in their development.
- Vertebrates are a subphylum of chordates that have a backbone (vertebral column).
- Therefore, all vertebrates (those with a backbone) are indeed chordates (those with a notochord), but not all chordates are vertebrates (as some, like tunicates and lancelets, do not develop a backbone).

**Conclusion:** This statement is true.

### Step 2: Analyze Statement 2
**Statement:** All craniates are vertebrates, but all vertebrates are not craniates.

**Explanation:**
- Craniates are animals that possess a skull (cranium). This group includes all vertebrates.
- Vertebrates have a backbone and are a subset of craniates.
- However, some extinct groups may not fit neatly into the category of vertebrates, but they are still considered craniates.

**Conclusion:** This statement is also true.

### Step 3: Analyze Statement 3
**Statement:** All flatworms possess metamerism, but all metamerically segmented organisms are not flatworms.

**Explanation:**
- Metamerism refers to the segmentation of the body into repeated units or segments.
- Flatworms (phylum Platyhelminthes) do not exhibit true metamerism; they are unsegmented.
- However, organisms like earthworms (phylum Annelida) do show metameric segmentation, and they are not flatworms.

**Conclusion:** This statement is false.

### Final Conclusion
Based on the analysis:
- Statement 1 is true.
- Statement 2 is true.
- Statement 3 is false.

Thus, the correct answer is that statements 1 and 2 are true, while statement 3 is false.

### Answer:
The correct answer is that statements 1 and 2 are true, and statement 3 is false.

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