Name one filamentous algae.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Concept of Filamentous Algae**:
- Filamentous algae are a type of algae that have a thread-like or chain-like structure. They are made up of cells that are joined end to end, forming long filaments.

2. **Characteristics of Algae**:
- Algae are primitive plants that do not have roots, stems, or leaves. They contain photosynthetic cells, which means they can produce their own food through the process of photosynthesis.

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