One of the following is a coelenterate

Options

A. Sea Fan
B. Sea Dollar
C. Sea Cucumber
D. Sea Horse.

Answer

To determine which of the following is a coelenterate, we need to analyze each option provided:

1. **Coral**: Corals are indeed coelenterates and belong to the phylum Cnidaria. They are known for producing calcium carbonate structures, which form coral reefs. Therefore, this option is correct.

2. **Sea Dollar**: Sea dollars are not coelenterates; they are echinoderms, which belong to the phylum Echinodermata. Therefore, this option is incorrect.

3. **Sea Cucumber**: Sea cucumbers are also echinoderms and belong to the phylum Echinodermata. Thus, this option is incorrect as well.

4. **Seahorse**: Seahorses are fish and belong to the class Actinopterygii within the phylum Chordata. Therefore, this option is also incorrect.

Based on the analysis above, the only correct option that represents a coelenterate is **Coral**.

### Summary of the Solution:
- **Coral**: Correct (Coelenterate, Phylum Cnidaria)
- **Sea Dollar**: Incorrect (Echinoderm, Phylum Echinodermata)
- **Sea Cucumber**: Incorrect (Echinoderm, Phylum Echinodermata)
- **Seahorse**: Incorrect (Fish, Phylum Chordata)

**Correct Answer**: Coral (Option 1)