Arms, pedicellariae and spines are absent in the echinoderm

Options

A. Star Fish
B. Sea Cucumber
C. Sea Lily
D. Sea Urchin.

Answer

To solve the question "Arms, pedicellariae, and spines are absent in the echinoderm," we need to analyze the given options one by one.

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Arms**: These are the appendages that some echinoderms, like starfish, have.
- **Pedicellariae**: These are small pincer-like structures found on some echinoderms, used for defense and cleaning.
- **Spines**: These are hard, pointed structures that can be found on the surface of some echinoderms.

2. **Evaluate the Options**:
- **Starfish**:
- Starfish have arms (usually five).
- They also possess spines and pedicellariae.
- **Conclusion**: Starfish do not fit the criteria.

- **Sea Cucumber**:
- Sea cucumbers belong to the class Holothuroidea.
- They do not have arms.
- They do not possess spines.
- They also lack pedicellariae.
- **Conclusion**: Sea cucumber fits the criteria as it lacks all three structures.

- **Sea Lily**:
- Sea lilies do not have spines.
- They lack pedicellariae.
- However, they do have branched arms.
- **Conclusion**: Sea lily does not fit the criteria due to the presence of arms.

- **Sea Urchin**:
- Sea urchins do not have arms.
- They do have spines and pedicellariae.
- **Conclusion**: Sea urchin does not fit the criteria.

3. **Final Decision**:
- After evaluating all options, the only echinoderm that lacks arms, pedicellariae, and spines is the **sea cucumber**.

### Answer:
The echinoderm that lacks arms, pedicellariae, and spines is the **sea cucumber**.

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