Which among the following is exclusively marine?

Options

A. Porifera
B. Echinodermata
C. Mollusca
D. Pisces

Explanation

**Step-by-Step Solution:**

1. **Understand the Question**: The question asks which of the given options is exclusively marine, meaning it only exists in marine environments (saline water) and not in freshwater or terrestrial habitats.

2. **Analyze the Options**: The options provided include:
- Porifera
- Echinodermata
- Mollusca
- Pisces

3. **Evaluate Porifera**:
- Porifera, which includes sponges, are primarily found in marine environments, but there are exceptions. Some sponges can exist in freshwater. Therefore, Porifera is not exclusively marine.

4. **Evaluate Echinodermata**:
- Echinodermata includes organisms like starfish and sea urchins. All members of this phylum are found exclusively in marine environments. There are no freshwater species in this group, making it a strong candidate.

5. **Evaluate Mollusca**:
- Mollusca includes a wide variety of organisms such as snails, clams, and octopuses. While many mollusks are marine, there are also freshwater and terrestrial species. Thus, Mollusca is not exclusively marine.

6. **Evaluate Pisces**:
- Pisces refers to fish, which can be divided into bony and cartilaginous fish. Many species of fish inhabit freshwater environments, so Pisces is not exclusively marine.

7. **Conclusion**: After evaluating all the options, the only group that is exclusively marine is Echinodermata. Therefore, the correct answer is **Echinodermata**.

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