Animlas which are triploblatic with tube- within - tube type of body plan and embryonic blastopore forms anus (deutterostomia ) are

Options

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

Answer

To solve the question regarding animals that are triploblastic with a tube-within-tube body plan and whose embryonic blastopore forms the anus (deuterostomia), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Triploblastic Animals:**
- Triploblastic animals have three germ layers: ectoderm, mesoderm, and endoderm. This characteristic is present in all the options provided (annelids, mollusca, platyhelminthes, echinodermata).

2. **Identifying the Body Plan:**
- The question specifies a "tube-within-tube" body plan. This type of body plan is characteristic of animals with a complete digestive system, where the inner tube represents the gut and the outer tube represents the body wall.
- Platyhelminthes (flatworms) do not have a tube-within-tube body plan; they have a blind sac body plan. Therefore, we can rule out option C (platyhelminthes).

3. **Determining Deuterostomia:**
- The term "deuterostomia" refers to a group of animals in which the blastopore (the first opening that forms during embryonic development) becomes the anus, while the mouth develops later.
- Echinodermata (such as starfish) and chordates (which include vertebrates) are examples of deuterostomes.

4. **Ruling Out Other Options:**
- Annelids (segmented worms) and mollusca (snails, clams, etc.) are classified as protostomes, meaning their blastopore develops into the mouth first. Therefore, options A (annelids) and B (mollusca) can also be ruled out.

5. **Final Answer:**
- Since echinodermata is the only group left that is triploblastic, has a tube-within-tube body plan, and is classified as deuterostomia, the correct answer is option D (echinodermata).

### Conclusion:
The animals which are triploblastic with a tube-within-tube type of body plan and whose embryonic blastopore forms the anus (deuterostomia) are **echinodermata**.