In dinophyceae, sulcus is

Options

A. Transverse flagellum
B. Longitudinal flagellum
C. Transverse groove
D. Longitudinal groove.

Answer

To answer the question regarding the sulcus in Dinophyceae, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dinophyceae**: Begin by recognizing that Dinophyceae, commonly known as dinoflagellates, are a group of unicellular eukaryotes that are primarily found in marine and freshwater environments.

2. **Identifying Key Terms**: The term "sulcus" is essential to this question. In the context of dinoflagellates, the sulcus refers to a specific groove or indentation on the cell surface.

3. **Options Analysis**: The options provided are:
- Transverse flagellum
- Longitudinal flagellum
- Transverse groove
- Longitudinal groove

4. **Understanding the Structure**: In dinoflagellates, the sulcus is characterized as a longitudinal groove. It extends from the annulus (a ring-like structure) posteriorly to the point where the second flagellum is attached.

5. **Differentiating Between Terms**: It's important to note that the sulcus is not a flagellum. Instead, it is a groove. The transverse groove in dinoflagellates is referred to as the cingulum, which is distinct from the sulcus.

6. **Conclusion**: Based on the definitions and structural characteristics, the correct answer to the question "In Dinophyceae, sulcus is" is **longitudinal groove**.

### Final Answer:
The sulcus in Dinophyceae is a **longitudinal groove**.

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