Which one exhibits concentric tube-within-tube plan ?
(a) Arthropoda
(b) Oligochaeta /Earthworm
(c) Mollusca
(d) Echinodermata

Options

A. Arthropoda
B. Oligochaeta /Earthworm
C. Mollusca
D. Echinodermata

Answer

To determine which organism exhibits a concentric tube-within-tube plan, we can analyze the options provided:

1. **Understanding the Tube-Within-Tube Plan**:
- The term "tube within tube" refers to a body plan where there is a body cavity (coelom) filled with fluid between the outer body wall and the inner gut wall. This is a characteristic feature of certain animal phyla.

2. **Evaluating the Options**:
- **(a) Arthropoda**: This phylum includes insects, arachnids, and crustaceans. They have an exoskeleton and do not exhibit a true coelomate body plan.
- **(b) Oligochaeta/Earthworm**: Earthworms belong to this class and are known for having a true coelom, which is a fluid-filled cavity between the body wall and the gut wall. This supports the tube-within-tube structure.
- **(c) Mollusca**: Mollusks have a coelom, but their body plan is not typically described as a tube-within-tube. They have a different arrangement of body structures.
- **(d) Echinodermata**: This phylum includes starfish and sea urchins. They have a unique body plan and do not exhibit the tube-within-tube arrangement.

3. **Conclusion**:
- Based on the analysis, the organism that exhibits the concentric tube-within-tube plan is **(b) Oligochaeta/Earthworm**.

**Final Answer**: (b) Oligochaeta/Earthworm

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