........... involves the fusion of two naked gametes, one or both of which are motile.

Explanation

To solve the question, we need to identify the process that involves the fusion of two naked gametes, where one or both of the gametes are motile. Here’s the step-by-step solution:

### Step 1: Understand the Key Terms
- **Naked Gametes**: These are gametes that are not surrounded by any protective structures.
- **Motile Gametes**: These are gametes that have the ability to move, typically through the use of flagella or cilia.

### Step 2: Identify the Process
- The question is asking for a specific type of reproduction that involves the fusion of these gametes.
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