Jointed arms occur in

Options

A. Echinus
B. Cucumaria
C. Ophiothrix
D. Echinoarachinus.

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks which group of organisms within the phylum Echinodermata has jointed arms.

2. **Identifying the Classes of Echinodermata**: Echinodermata is divided into several classes, including:
- Asteroidea (starfish)
- Ophiuroidea (brittle stars)
- Echinoidea (sea urchins)
- Holothuroidea (sea cucumbers)
- Crinoidea (sea lilies)

3. **Analyzing Each Class**:
- **Asteroidea**: Starfish have arms but they are not jointed.
- **Echinoidea**: Sea urchins have a hard shell and do not have jointed arms.
- **Holothuroidea**: Sea cucumbers have elongated bodies and do not possess jointed arms.
- **Crinoidea**: Sea lilies have feathery arms but they are not jointed.

4. **Identifying the Correct Class**: The class that contains organisms with jointed arms is **Ophiuroidea**, which includes brittle stars.

5. **Conclusion**: The correct answer to the question is that jointed arms occur in **Ophiuroidea**, specifically in brittle stars.

6. **Final Answer**: The organism with jointed arms is **Ophiuroidea (brittle stars)**.

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