Radial symmetry of echinoderms is

Options

A. primary
B. Secondary
C. Biradial
D. Triradial.

Answer

**Step-by-Step Solution:**

1. **Understanding Echinoderms**: Echinoderms are a group of marine animals that include starfish, sea urchins, and sea cucumbers. They exhibit a unique body structure.

2. **Defining Radial Symmetry**: Radial symmetry means that the body can be divided into similar halves by multiple planes passing through the central axis. This is different from bilateral symmetry, where the body can only be divided into two similar halves.

3. **Identifying the Symmetry in Echinoderms**: Echinoderms exhibit radial symmetry in their adult form. However, it is important to note that their larvae are bilaterally symmetrical.

4. **Primary vs. Secondary Symmetry**: The term "primary symmetry" refers to the symmetry present in the early developmental stages. In the case of echinoderms, their larvae show bilateral symmetry (primary), while adults show radial symmetry (secondary).

5. **Evaluating the Options**:
- **Primary**: Incorrect, as adult echinoderms do not have bilateral symmetry.
- **Secondary**: Correct, as adult echinoderms exhibit radial symmetry, which develops after the bilateral symmetry of the larval stage.
- **Biradial**: Incorrect, as echinoderms do not fit this classification.
- **Triradial**: Incorrect, as echinoderms are typically described as having pentaradial symmetry, not triradial.

6. **Conclusion**: The correct answer is that the radial symmetry of echinoderms is secondary.

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