The members of which of the following phyla are exclusively marine ?

Options

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

Answer

To determine which phylum has members that are exclusively marine, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Options**:
- A. Orthopoda
- B. Echinodermata
- C. Annelida
- D. Mollusca

2. **Analyzing Orthopoda**:
- Members of the phylum Arthropoda (which includes insects, arachnids, and crustaceans) can be found in various environments, including terrestrial, freshwater, and marine habitats. Therefore, this phylum is not exclusively marine.

3. **Analyzing Echinodermata**:
- Members of the phylum Echinodermata, such as starfish and sea cucumbers, are exclusively marine. They are found only in oceanic environments. This phylum is characterized by features such as an endoskeleton made of calcareous ossicles, triploblastic organization, and a unique water vascular system. Hence, this phylum is exclusively marine.

4. **Analyzing Annelida**:
- The phylum Annelida includes segmented worms, which can be found in marine, freshwater, and terrestrial environments. Therefore, this phylum is not exclusively marine.

5. **Analyzing Mollusca**:
- Mollusca includes a diverse group of animals such as snails, clams, and octopuses. Members of this phylum can inhabit marine, freshwater, and terrestrial environments. Thus, this phylum is also not exclusively marine.

6. **Conclusion**:
- After analyzing all the options, we find that the only phylum with members that are exclusively marine is **B. Echinodermata**.

### Final Answer:
**B. Echinodermata**