Which colourless protistan shows bioluminescence?

Options

A. Navicula
B. Noctiluca
C. Dictyostelium
D. Phacus

Answer

### Step-by-Step Solution:

1. **Understanding Bioluminescence**:
- Bioluminescence is the ability of an organism to produce and emit light. This phenomenon is typically due to biochemical reactions that occur within the organism.

2. **Identifying the Options**:
- The question provides four options:
1. Navicula
2. Noctiluca
3. Dictyosterium
4. Fraccus

3. **Analyzing Each Option**:
- **Navicula**: This is a genus of diatoms and does not exhibit bioluminescence.
- **Noctiluca**: This is a dinoflagellate known for its bioluminescent properties, especially when disturbed by movement in water.
- **Dictyosterium**: This is a genus of slime molds and does not show bioluminescence.
- **Fraccus**: This is not a well-known genus associated with bioluminescence.

4. **Conclusion**:
- Among the options, **Noctiluca** (specifically Noctiluca scintillans) is the only colorless protistan that exhibits bioluminescence. It emits light in response to mechanical stimuli, such as agitation of water.

5. **Final Answer**:
- The colorless protistan that shows bioluminescence is **Noctiluca**.