A sedentary echinoderm is

Options

A. sea lily
B. Sea pen
C. Sea urchin
D. sea cucumber

Answer

To determine which of the given options is a sedentary echinoderm, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Sedentary Echinoderms**: Sedentary echinoderms are organisms that are attached to a substratum (the surface they live on) and do not move around freely.

2. **Review the Options**: The options provided are:
- A) Sea lily
- B) Sea pen
- C) Sea urchin
- D) Sea cucumber

3. **Identify Characteristics of Each Option**:
- **Sea Lily (Antedon)**: This is a type of echinoderm that is typically attached to the sea floor and remains in one place, making it a sedentary organism.
- **Sea Pen**: This is actually a cnidarian, not an echinoderm, so it is not a valid option.
- **Sea Urchin (Echinus)**: Sea urchins are generally mobile and do not fit the definition of sedentary.
- **Sea Cucumber (Holothuroidea)**: While they can be found on the sea floor, they are not typically considered sedentary as they can move slowly.

4. **Conclusion**: Based on the characteristics and definitions, the only option that fits the criteria of a sedentary echinoderm is the **Sea Lily (Antedon)**.

### Final Answer:
A sedentary echinoderm is **Sea Lily (Antedon)**.

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