Exoskeleton of echinoderms is

Options

A. Chitinous
B. Siliceous
C. Calcareous
D. None of the above.

Answer

### Step-by-Step Solution:

1. **Understanding Echinoderms**: Echinoderms are marine animals belonging to the phylum Echinodermata, which includes starfish, sea urchins, and sea cucumbers.

2. **Identifying the Exoskeleton**: The question asks about the type of exoskeleton present in echinoderms. An exoskeleton is a hard outer structure that provides support and protection to the organism.

3. **Options Given**: The options provided are:
- A) Cutaneous
- B) Siliceous
- C) Calcareous
- D) None of the above

4. **Analyzing Each Option**:
- **Cutaneous**: This refers to a skin-like covering, not applicable to echinoderms.
- **Siliceous**: This type of exoskeleton is found in organisms like diatoms and some sponges, not echinoderms.
- **Calcareous**: This refers to structures made of calcium carbonate, which is indeed the composition of the exoskeleton in echinoderms.
- **None of the above**: This option can be disregarded since we have identified a suitable option.

5. **Conclusion**: Based on the analysis, the correct answer is **C) Calcareous**. The exoskeleton of echinoderms is primarily made up of calcium carbonate.