Batrachospermum is a

Options

A. red algae of sea
B. brown algae
C. blue algae
D. red algae of freshwater

Explanation

**Step-by-Step Solution:**

1. **Identify the Organism**: The question asks about Batrachospermum. We need to determine what type of organism it is.

2. **Classification**: Batrachospermum belongs to the group known as red algae. This classification places it within the division Rhodophyta.

3. **Family Identification**: Within the red algae, Batrachospermum is part of the family Betrachospermiaceae. This helps narrow down its classification further.

4. **Habitat**: Batrachospermum typically inhabits freshwater environments, specifically in slow-moving water bodies like lakes and ponds. This is important for understanding its ecological niche.

5. **Body Structure**: The organism has a branched structure with thread-like filaments. This morphological characteristic is typical for many types of algae.

6. **Color Variation**: The color of Batrachospermum can vary based on light intensity, ranging from violet to blue-green. This indicates its adaptability to different light conditions.

7. **Conclusion**: Based on the classification, habitat, and characteristics discussed, we can conclude that Batrachospermum is a type of red algae that lives in freshwater.

8. **Final Answer**: Therefore, the correct description of Batrachospermum is that it is a red algae of freshwater.