The only positive evidence to aquatic ancestry of Bryophytes is

Options

A. Their green colour
B. Thread-like protonema
C. Ciliated sperms
D. Some forms are still aquatic.

Answer

### Step-by-Step Text Solution:

1. **Understanding Bryophytes**:
- Bryophytes are the simplest land plants and are categorized into two main groups: mosses and liverworts. They are non-vascular plants, meaning they lack specialized tissues for transporting water and nutrients.

2. **Aquatic Ancestry**:
- The question asks for evidence supporting the aquatic ancestry of bryophytes. Aquatic ancestry implies that these plants evolved from ancestors that lived in water.

3. **Reproductive Characteristics**:
- Bryophytes reproduce through a process that requires water for fertilization. The male gametes (sperms) need to swim through water to reach the female gametes (eggs) for fertilization to occur.

4. **Ciliated Sperm**:
- The sperm of bryophytes are often ciliated, which means they have hair-like structures that enable them to swim in water. This adaptation is crucial for their reproduction in aquatic environments.

5. **Conclusion**:
- The presence of ciliated sperm is a significant piece of evidence indicating that bryophytes have an aquatic ancestry. This is because these ciliated sperms are adapted to move through water, which is a characteristic of organisms that reproduce in aquatic habitats.

6. **Final Answer**:
- Therefore, the only positive evidence of the aquatic ancestry of bryophytes is **ciliated sperms**.