Identify the respective phylum to which the following organisms belong. Give their characteristics.
Small green threads sticking to rocks in water bodies.

Explanation

**Step-by-Step Solution:**

1. **Identify the Organism**: The small green threads sticking to rocks in water bodies are identified as algae.

2. **Determine the Phylum**: Algae belong to the phylum Thallophyta. This is because they have a simple structure known as a thallus, which is not differentiated into true roots, stems, or leaves.

3. **Classify the Sub-Phylum**: Within Thallophyta, algae fall under the sub-phylum Cryptogams. Cryptogams are characterized by their reproductive structures that do not produce seeds.

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