Compound eyes occur in

Options

A. Echinodermate
B. Mollusca
C. Arthropoda
D. Annelida

Answer

### Step-by-Step Solution:

1. **Understanding Compound Eyes**:
- Compound eyes are a specialized type of eye found in certain animals, particularly arthropods. They are made up of multiple small units called ommatidia.

2. **Identifying the Phylum**:
- The question asks where compound eyes occur. Compound eyes are characteristic features of the phylum Arthropoda, which includes insects, crustaceans, and arachnids.

3. **Structure of Compound Eyes**:
- Each compound eye consists of numerous ommatidia (hexagonal structures). Each ommatidium has two main parts: the dioptric part (for focusing light) and the receptive part (for detecting light).

4. **Vision Type**:
- The vision provided by compound eyes is known as mosaic vision, which allows for a detailed and three-dimensional perception of the environment.

5. **Exclusion of Other Phyla**:
- The question provides options that include Echinoderms, Mollusca, and Annelids. These groups do not possess compound eyes:
- **Echinoderms**: Typically lack eyes (some have simple light-sensitive spots).
- **Mollusca**: Generally have simple eyes or camera-type eyes, not compound.
- **Annelids**: Also do not have compound eyes.

6. **Conclusion**:
- Based on the characteristics and the exclusion of other phyla, the correct answer to the question "Compound eyes occur in" is option number 3, which refers to Arthropoda.