A sedentary sea anemone gets attached to the shell lining of hermit crab. The association is

Options

A. commensalism
B. Amensalism
C. Ectoparasitism
D. symbiosis

Explanation

To determine the type of association between a sedentary sea anemone and a hermit crab, we can analyze the definitions of the different types of ecological relationships provided in the question.

### Step-by-Step Solution:

1. **Understand the Organisms Involved**:
- The sea anemone is a sedentary organism that attaches itself to a surface.
- The hermit crab is a mobile organism that uses shells for protection.

2. **Identify the Nature of the Relationship**:
- The sea anemone benefits by having a place to attach and possibly gain access to food particles that the hermit crab may disturb while moving.
- The hermit crab is not harmed or benefited significantly by the presence of the sea anemone.

3. **Evaluate the Options**:
- **Commensalism**: One species benefits, and the other is neither helped nor harmed. This seems to fit the scenario since the anemone benefits while the crab is unaffected.
- **Amensalism**: One species is harmed while the other is unaffected. This does not apply here.
- **Ectoparasitism**: One organism lives on the surface of another and causes harm. This does not apply since the sea anemone does not harm the crab.
- **Symbiosis**: A mutually beneficial relationship. This does not apply since the crab does not gain a benefit from the anemone.

4. **Conclusion**:
- The correct association between the sedentary sea anemone and the hermit crab is **commensalism**.

### Final Answer:
The association is **commensalism**.

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