A colourless dinoflagellate which is also classified as protozoa :-

Options

A. Euglena
B. Ceratium
C. Noctiluca
D. Gonyaulax

Answer

To solve the question regarding a colorless dinoflagellate classified as protozoa, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Classification**: Begin by recognizing that dinoflagellates are a group of protists, and some of them can be classified as protozoa. We need to identify a colorless dinoflagellate that fits this classification.

2. **Evaluate the Options**: The options given are Euglena, Ceratium, Noctiluca, and Goniolax. We will analyze each option to determine which one fits the criteria of being a colorless dinoflagellate.

3. **Analyze Euglena**:
- Euglena is a unicellular organism and is classified as an euglenoid.
- It is biflagellate and has histones, which distinguishes it from dinoflagellates.
- Conclusion: **Euglena is not a dinoflagellate** and can be eliminated.

4. **Analyze Ceratium**:
- Ceratium is a dinoflagellate with a cell wall made of cellulose and is typically golden-brown in color.
- Since it is not colorless, we can eliminate this option as well.

5. **Analyze Noctiluca**:
- Noctiluca is known as a colorless dinoflagellate.
- It exhibits holozoic nutrition and bioluminescence due to the presence of the pigment luciferin.
- Importantly, Noctiluca lacks a cell wall, which allows it to be classified as protozoa.
- Conclusion: **Noctiluca fits both criteria** of being a colorless dinoflagellate and classified as protozoa.

6. **Analyze Goniolax**:
- Goniolax is identified as a red dinoflagellate.
- Since it is red in color, it does not meet the requirement of being colorless.
- Conclusion: **Goniolax can be eliminated**.

7. **Final Answer**: After evaluating all the options, the correct answer is **Noctiluca**, as it is a colorless dinoflagellate that is classified as protozoa.

### Final Answer:
**Noctiluca**