The principal axis in radial symmetry is

Options

A. transverse
B. oro-aboral
C. sagittal
D. any axis

Answer

To answer the question regarding the principal axis in radial symmetry, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Radial Symmetry**:
- Radial symmetry is a type of symmetry where the body plan is arranged around a central axis. Organisms with radial symmetry can be divided into similar halves by multiple planes that pass through the central axis.

2. **Identifying the Organisms**:
- The question relates to organisms that exhibit radial symmetry, particularly focusing on the phylum Echinodermata, which includes starfish, sea urchins, and other similar marine animals.

3. **Defining the Principal Axis**:
- The principal axis in radial symmetry is the line that runs through the center of the organism, allowing for symmetrical division. In the case of echinoderms, this axis is crucial for understanding their structure.

4. **Determining the Faces**:
- Echinoderms typically have two main surfaces: the oral surface (where the mouth is located) and the aboral surface (where the anus is located). These surfaces are crucial in defining the principal axis.

5. **Identifying the Correct Option**:
- In the context of the question, the principal axis in radial symmetry for echinoderms is aligned with the oral surface and the aboral surface. Therefore, the correct answer is "oral or aboral".

6. **Conclusion**:
- The principal axis in radial symmetry is the line that runs between the oral and aboral surfaces, which is essential for the symmetrical arrangement of the organism.

### Final Answer:
The principal axis in radial symmetry is **oral or aboral**.

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