Which cnidarians possess a skeleton made up of calcium carbonate?

Answer

**Step-by-Step Solution:**

1. **Understanding Cnidarians**: Begin by defining what cnidarians are. Cnidarians are a group of marine animals that include organisms such as jellyfish, sea anemones, and corals. They are characterized by their radial symmetry and the presence of specialized cells known as nematocytes.

2. **Identifying Key Features**: Note that cnidarians possess nematocytes, which are stinging cells used for defense and capturing prey. This is a unique feature of this group of animals.

3. **Focusing on the Skeleton**: The question specifically asks about cnidarians that have a skeleton made of calcium carbonate. This is an important detail to focus on.

4. **Recognizing Calcium Carbonate Skeletons**: Among cnidarians, certain types have skeletons composed of calcium carbonate. The most notable examples of these are corals.

5. **Conclusion**: Therefore, the cnidarians that possess a skeleton made up of calcium carbonate are corals.

**Final Answer**: Corals.

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