The sulcus or longitudinal groove of dinophycean shell contains

Options

A. Narrow smooth flagellum
B. Thick ribbon -shaped flagellum
C. Tail
D. Mucilage canal.

Answer

To answer the question regarding what the sulcus or longitudinal groove of the dinophycean shell contains, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dinophyceae**:
- Dinophyceae, commonly known as dinoflagellates, are a group of unicellular eukaryotes that are characterized by their unique cell structure, which includes a shell or theca.

2. **Identifying the Structure**:
- The dinoflagellate cell surface features two distinct grooves or furrows: the transverse furrow (cingulum) and the longitudinal furrow (sulcus).

3. **Focusing on the Sulcus**:
- The sulcus is the longitudinal groove that runs along the body of the dinoflagellate. It is important to identify what is located within this groove.

4. **Analyzing the Options**:
- The options provided are:
- A) Narrow smooth flagellum
- B) Thick ribbon-shaped flagellum
- C) Tail
- D) Mucilage canal

5. **Determining the Correct Answer**:
- The sulcus contains a narrow, smooth flagellum. This flagellum is thread-like and plays a crucial role in the locomotion of the dinoflagellate.
- The transverse groove (cingulum) also contains a flagellum, but it is distinct from the one in the sulcus.

6. **Conclusion**:
- Therefore, the correct answer to the question is that the sulcus or longitudinal groove of the dinophycean shell contains a **narrow smooth flagellum**.

### Final Answer:
The sulcus or longitudinal groove of the dinophycean shell contains a **narrow smooth flagellum**.

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