Which of the following statements is incorrect with regard to bilateral symmetry?

Options

A. Body can be divided into two equal halves by a single plane only.
B. The organisms that show bilateral symmetry have paired body organs that occur on the two sides of a central axis.
C. It is found in all invertebrates and few vertebrates.
D. Spider and crab show bilateral symmetery.

Explanation

To determine which statement is incorrect regarding bilateral symmetry, let's analyze each statement step by step.

### Step 1: Understand Bilateral Symmetry
Bilateral symmetry refers to a body plan in which an organism can be divided into two equal halves along a single plane. This means that there is a distinct right and left side that are mirror images of each other.

### Step 2: Analyze Each Statement
1. **Statement 1**: "Body can be divided into two equal halves by a single plane only."
- This statement is true. Bilateral symmetry allows for division into two equal halves along one specific plane.

2. **Statement 2**: "The organism that shows bilateral symmetry have paired body organs that can occur on the two sides of the central axis."
- This statement is also true. Organisms with bilateral symmetry typically have paired organs (like eyes, limbs) on either side of their body.

3. **Statement 3**: "It is found in all invertebrates and few vertebrates."
- This statement is incorrect. Bilateral symmetry is not found in all invertebrates; it is primarily found in some invertebrates and all vertebrates (including all chordates).

4. **Statement 4**: "Spider and crab show bilateral symmetry."
- This statement is true. Both spiders and crabs, which belong to the phylum Arthropoda, exhibit bilateral symmetry.

### Conclusion
The incorrect statement regarding bilateral symmetry is **Statement 3**: "It is found in all invertebrates and few vertebrates."

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