What are choanocytes? Give their function.

Explanation

### Step-by-Step Solution:

1. **Definition of Choanocytes**:
- Choanocytes, also known as collar cells, are specialized cells found in sponges, which belong to the phylum Porifera. They are characterized by a unique collar-like structure.

2. **Structure of Choanocytes**:
- Each choanocyte has a central flagellum surrounded by a collar of microvilli. This collar structure helps in trapping food particles from the water.

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