Among the following which one is not a deuterostome?

Options

A. Sea urchin
B. Earthworm
C. Sand dollar
D. Ichthyophis

Answer

To determine which of the following options is not a deuterostome, we need to understand what deuterostomes are and identify the classification of each option provided.

### Step-by-Step Solution:

1. **Understanding Deuterostomes**:
- Deuterostomes are a group of animals characterized by their embryonic development. In these organisms, the anus forms before the mouth during early development. This is in contrast to protostomes, where the mouth develops first.

2. **Identifying the Options**:
- Let's evaluate each option to see if they belong to the deuterostome group.

3. **Option 1: Sea Urchin**:
- Sea urchins belong to the phylum Echinodermata. Echinoderms are deuterostomes. Therefore, this option is not the correct answer.

4. **Option 2: Earthworm**:
- Earthworms belong to the phylum Annelida. Annelids are classified as protostomes, which means they develop the mouth before the anus. Thus, this option is the correct answer as it is not a deuterostome.

5. **Option 3: Sand Dollar**:
- Sand dollars are also part of the phylum Echinodermata, similar to sea urchins. Therefore, they are deuterostomes. This option is not the correct answer.

6. **Option 4: Ichthyophis**:
- Ichthyophis is a genus of caecilians, which belong to the phylum Chordata. Chordates are deuterostomes. Thus, this option is also not the correct answer.

7. **Conclusion**:
- The only option that is not a deuterostome is **Option 2: Earthworm**.

### Final Answer:
**Option 2: Earthworm** is not a deuterostome.

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