Chitnous cuticle forms exoskeleton in
(a) Annelida
(b) Echinodermata
(c) Porifera
(d) Arthropoda

Options

A. Annelida
B. Echinodermata
C. Porifera
D. Arthropoda.

Answer

To solve the question regarding which phylum has a chitinous cuticle forming an exoskeleton, we will analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding the Question**:
- The question asks which phylum has a chitinous cuticle that forms an exoskeleton. An exoskeleton is an external skeleton that provides support and protection.

2. **Analyzing Option (a): Annelida**:
- Annelids, such as earthworms, do not possess a chitinous exoskeleton. Instead, they have a segmented body covered by a moist cuticle, but it is not a hard exoskeleton. Therefore, this option is incorrect.

3. **Analyzing Option (b): Echinodermata**:
- Echinoderms, like starfish and sea urchins, have an endoskeleton made of calcareous materials (calcium carbonate). They do not have a chitinous exoskeleton. Hence, this option is also incorrect.

4. **Analyzing Option (c): Porifera**:
- Porifera, or sponges, have a skeletal structure that can be made up of silica or calcium carbonate, but they do not possess a chitinous exoskeleton. Therefore, this option is incorrect as well.

5. **Analyzing Option (d): Arthropoda**:
- Arthropods, which include insects, arachnids, and crustaceans, have a well-defined exoskeleton made of chitin. This chitinous cuticle provides protection and support to their bodies. Thus, this option is correct.

6. **Conclusion**:
- The correct answer is (d) Arthropoda, as they are the only phylum listed that possesses a chitinous cuticle forming an exoskeleton.

### Final Answer:
(d) Arthropoda