In which of the following phylum all the animals are exclusively marine with organ system level of organisation?

Options

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

Explanation

To solve the question "In which of the following phylum all the animals are exclusively marine with organ system level of organisation?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a phylum where all animals are exclusively marine and possess an organ system level of organization.

2. **Review the Options**: The options given are:
- A) Silentrata
- B) Porifera
- C) Echinodermata
- D) Mollusca

3. **Analyze Each Option**:
- **Silentrata**: This phylum includes organisms like jellyfish and corals. While many are marine, not all are exclusively marine. Therefore, this option is incorrect.

- **Porifera**: This phylum consists of sponges, which have a cellular level of organization, not an organ system level. Thus, this option is also incorrect.

- **Echinodermata**: This phylum includes starfish, sea urchins, and sea cucumbers. All members are exclusively marine and they exhibit an organ system level of organization. This option is correct.

- **Mollusca**: This phylum includes snails, clams, and octopuses. While many are marine, there are also freshwater and terrestrial forms. Therefore, this option is incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is **Echinodermata**, as it is the only phylum where all members are exclusively marine and possess an organ system level of organization.

### Final Answer:
The correct answer is **Echinodermata**.

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