Which of the following animals has tube- within-tube type of body plan evolved along deuterostomic evolutionary line ?

Options

A. Annelids
B. Arthropods
C. Echinoderms
D. Molluscs

Explanation

To determine which animal has a tube-within-tube type of body plan evolved along the deuterostomic evolutionary line, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Tube-Within-Tube Body Plan**:
- The tube-within-tube body plan refers to organisms that have a complete digestive tract, which consists of two openings: one for ingestion (mouth) and one for egestion (anus). This is also known as a complete digestive system.

2. **Identify the Key Characteristics of Deuterostomes**:
- Deuterostomes are characterized by their embryonic development where the anus forms before the mouth. This is a significant feature that distinguishes them from protostomes.

3. **Analyze the Given Options**:
- The options provided are:
- Annelids
- Arthropods
- Echinoderms
- Molluscs

4. **Evaluate Each Option**:
- **Annelids**: These belong to the protostome group, not deuterostomes.
- **Arthropods**: Also belong to the protostome group, hence not deuterostomes.
- **Echinoderms**: These are classified as deuterostomes and have a tube-within-tube body plan.
- **Molluscs**: These are protostomes, thus do not fit the criteria.

5. **Conclusion**:
- Based on the analysis, the only group among the options that fits the criteria of having a tube-within-tube body plan evolved along the deuterostomic evolutionary line is **Echinoderms**.

### Final Answer:
**Echinoderms**