The animal with bilateral symmetry in young stage and radial pentamerous symmetry in the adult stage belong to the phylum

Options

A. Annelida
B. Mollusca
C. Cnidaria
D. Echinodermata

Explanation

To solve the question regarding the animal that exhibits bilateral symmetry in its young stage and radial pentamerous symmetry in its adult stage, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Symmetry Types**:
- Bilateral symmetry means the organism can be divided into two identical halves along one plane. This is common in many animals during their early developmental stages.
- Radial symmetry, specifically pentamerous symmetry, means the organism can be divided into five equal parts around a central axis. This is often seen in adult forms of certain marine animals.

2. **Identify the Phylum**:
- We need to determine which phylum contains animals that transition from bilateral symmetry in their larval stage to radial pentamerous symmetry in their adult stage.

3. **Consider Examples**:
- Echinodermata is a phylum that includes starfish, sea urchins, and sea cucumbers.
- In the larval stage, echinoderms (like starfish) exhibit bilateral symmetry. As they mature into adults, they develop radial pentamerous symmetry.

4. **Eliminate Other Options**:
- Other phyla mentioned (like Annelida, Mollusca, and Cnidaria) typically maintain bilateral symmetry throughout their life stages or do not exhibit the specific transition described in the question.

5. **Conclusion**:
- Based on the characteristics and examples discussed, the correct answer is that the animal with bilateral symmetry in the young stage and radial pentamerous symmetry in the adult stage belongs to the phylum **Echinodermata**.

### Final Answer:
The animal with bilateral symmetry in the young stage and radial pentamerous symmetry in the adult stage belongs to the phylum **Echinodermata**.

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