In Echinodermata

Options

A. both larvae and adults are radially symmetrical
B. both larvate and adults are bilaterally symmetrical
C. larvae are radially symmetrical whereas adults are bilaterally symmetrical
D. larvae are bilaterally symmetrical whereas adults are radially symmetrical

Answer

### Step-by-Step Solution:

1. **Understanding Echinodermata**:
- Echinodermata are marine animals that include species such as sea stars, sea urchins, and sea cucumbers. They are exclusively found in the sea.

2. **Identifying Symmetry Types**:
- There are two main types of symmetry to consider: bilateral symmetry and radial symmetry.
- **Bilateral Symmetry**: An organism is bilaterally symmetrical if it can be divided into two equal halves along one plane. This means that there is only one way to split the organism into two identical parts.
- **Radial Symmetry**: An organism exhibits radial symmetry if it can be divided into similar halves by multiple planes that pass through the central axis. This means that there are multiple ways to split the organism into equal parts.

3. **Symmetry in Echinodermata**:
- In the **larval stage** of echinoderms, they exhibit **bilateral symmetry**. This means that during their early development, they can be divided into two equal halves along one plane.
- In the **adult stage**, echinoderms display **radial symmetry**. For example, a sea star has five arms and can be divided into equal parts through multiple planes that pass through its center.

4. **Conclusion**:
- Based on the observations, we conclude that:
- Larvae of echinoderms are bilaterally symmetrical.
- Adults of echinoderms are radially symmetrical.
- Therefore, the correct answer to the question is **option number 4**: "larvae are bilaterally symmetrical whereas adults are radially symmetrical."