Sulcus is

Options

A. Feeding apparatus of ciliates
B. Longitudinal groove of dinoflagellates
C. Transverse groove of dinoflagellates
D. Tentacle of Noctiluca

Answer

**Step-by-Step Solution:**

1. **Understanding the Term "Sulcus":**
- The term "sulcus" refers to a specific structure found in certain organisms, particularly dinoflagellates.

2. **Identifying the Organism:**
- Sulcus is associated with dinoflagellates, which are a group of single-celled organisms known for their two flagella and unique cellular structures.

3. **Defining Sulcus:**
- In dinoflagellates, the sulcus is described as a longitudinal groove or furrow on the cell surface.

4. **Differentiating Between Grooves:**
- It is important to note that dinoflagellates have both a longitudinal groove (sulcus) and a transverse groove (called the cingulum). The sulcus runs along the length of the organism.

5. **Analyzing the Options:**
- The question provides multiple-choice options regarding what sulcus is.
- The first option states it is a feeding apparatus of ciliates, which is incorrect.
- The second option correctly identifies sulcus as the longitudinal grooves of dinoflagellates.
- The third option incorrectly describes it as a transverse groove, which is known as cingulum.
- The fourth option mentions tentacles of noctiluca, which is also incorrect.

6. **Conclusion:**
- Based on the definitions and explanations, the correct answer to the question "Sulcus is" is that it is the longitudinal groove of dinoflagellates.

**Final Answer:**
- Sulcus is the longitudinal groove of dinoflagellates.

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