The cell wall is absent in

Options

A. (a) dinoflagellates
B. (b) diatoms
C. (c) euglenoids
D. (d) none of these

Answer

To solve the question "The cell wall is absent in," we will analyze each option provided:

1. **Understanding the Options**:
- A. Dinoflagellates
- B. Diatoms
- C. Euglenoids
- D. None of the above

2. **Analyzing Dinoflagellates**:
- Dinoflagellates are unicellular organisms that belong to the kingdom Protista. They possess a cell wall, which is primarily made up of cellulose and is referred to as "theca" or "cica." Therefore, dinoflagellates do have a cell wall.

3. **Analyzing Diatoms**:
- Diatoms are also unicellular organisms in the kingdom Protista. They have a unique cell wall composed of silica, which gives them a glass-like structure. Thus, diatoms also possess a cell wall.

4. **Analyzing Euglenoids**:
- Euglenoids are another group of unicellular organisms within the kingdom Protista. Unlike dinoflagellates and diatoms, euglenoids do not have a rigid cell wall. Instead, they have a flexible protein covering known as a pellicle. This allows them to change shape and is a distinguishing feature of euglenoids.

5. **Conclusion**:
- Based on the analysis, we find that both dinoflagellates and diatoms have cell walls, while euglenoids do not have a proper cell wall. Therefore, the correct answer to the question "The cell wall is absent in" is option C: Euglenoids.

### Final Answer:
C. Euglenoids