In which phylum organisms alter their symmetry from bilateral to radial during the development?

Answer

To answer the question, "In which phylum do organisms alter their symmetry from bilateral to radial during development?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand Symmetry Types**:
- **Bilateral Symmetry**: This type of symmetry means that the organism can be divided into two identical halves along one plane. Examples include humans and butterflies.
- **Radial Symmetry**: This type of symmetry allows the organism to be divided into multiple identical parts around a central axis. Examples include jellyfish and sea anemones.

2. **Identify the Phylum**:
- The question specifically asks for a phylum where organisms transition from bilateral symmetry to radial symmetry during their development.

3. **Recognize the Key Phylum**:
- The phylum that exhibits this change is **Echinodermata**.

4. **Developmental Stages**:
- In Echinodermata, the larval stage exhibits bilateral symmetry. As the organism develops into its adult form, it undergoes a transformation where it exhibits radial symmetry.

5. **Conclusion**:
- Therefore, the answer to the question is that organisms in the phylum **Echinodermata** alter their symmetry from bilateral to radial during their development.

### Final Answer:
The phylum in which organisms alter their symmetry from bilateral to radial during development is **Echinodermata**.