Bilateral symmetry does not occur in

Options

A. Frog
B. Octopus
C. Mammal
D. Obelia.

Answer

To determine which organism does not exhibit bilateral symmetry, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Bilateral Symmetry**:
- Bilateral symmetry refers to a body plan in which the left and right halves of an organism are mirror images of each other when divided along the anteroposterior axis. This means that if you were to cut the organism down the middle, both halves would look the same.

2. **Analyze the Options**:
- **Option 1: Frog**: Frogs are amphibians and exhibit bilateral symmetry. Their body can be divided into two symmetrical halves.
- **Option 2: Octopus**: Octopuses are cephalopods and also exhibit bilateral symmetry. Their body structure allows for a left and right side that mirror each other.
- **Option 3: Mammal**: Mammals, including humans, exhibit bilateral symmetry. Their body structures are organized in a way that allows for symmetrical halves.
- **Option 4: Obelia**: Obelia is a colonial organism belonging to the class Hydrozoa within the phylum Coelenterata (Cnidaria). Organisms in this group typically exhibit radial symmetry, meaning their body parts are arranged around a central axis.

3. **Identify the Organism Without Bilateral Symmetry**:
- Based on the analysis, Obelia is the only organism listed that does not exhibit bilateral symmetry. Instead, it has radial symmetry.

4. **Conclusion**:
- Therefore, the answer to the question "Bilateral symmetry does not occur in" is **Obelia**.