Sea water glows during night mainly due to occurrence of
(a) Gonyaulax
(b) Noctiluca
(c) Euglena
(d) Cyclotella

Options

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

Answer

To determine why seawater glows during the night, we need to analyze the options provided and understand the biological classification of the organisms involved.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks why seawater glows at night. This phenomenon is typically due to certain microorganisms that exhibit bioluminescence.

2. **Analyzing the Options**:
- **(a) Gonyaulax**: This is a genus of dinoflagellates, which are known to exhibit bioluminescence.
- **(b) Noctiluca**: This is another genus of dinoflagellates that is well-known for its luminescent properties, especially at night.
- **(c) Euglena**: While Euglena is a flagellated protist and can photosynthesize, it is not primarily known for bioluminescence.
- **(d) Cyclotella**: This is a genus of diatoms, which do not exhibit bioluminescence.

3. **Identifying the Correct Answer**:
- The organisms responsible for the glowing of seawater at night are primarily dinoflagellates, specifically **Noctiluca**.
- Although **Gonyaulax** also has luminescent properties, **Noctiluca** is the most commonly recognized for this phenomenon.

4. **Conclusion**: The correct answer to the question is **(b) Noctiluca**.

### Final Answer:
(b) Noctiluca

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