Mesokaryotic organization is found in :

Options

A. Euglena
B. Diatoms
C. Dinoflagellates
D. All of these

Answer

### Step-by-Step Solution

1. **Understanding Mesokaryotic Organization**:
- Mesokaryotic organization refers to a type of cellular organization that is intermediate between prokaryotic and eukaryotic cells. These cells possess a well-defined nucleus similar to eukaryotes, but the way the nucleus divides is more akin to prokaryotes.

2. **Identifying Characteristics**:
- Mesokaryotic cells have a well-developed nucleus.
- The nucleus divides by a process similar to binary fission, which is characteristic of prokaryotes.

3. **Analyzing the Options**:
- **Option 1: Euglena**:
- Euglena is a unicellular organism with a eukaryotic organization, not mesokaryotic. Therefore, this option is incorrect.
- **Option 2: Diatoms**:
- Diatoms are also unicellular or multicellular eukaryotic organisms with a silica cell wall. They do not exhibit mesokaryotic organization, making this option incorrect as well.
- **Option 3: Dinoflagellates**:
- Dinoflagellates are known to have mesokaryotic organization. They possess characteristics that fit the definition of mesokaryotic cells, thus this option is correct.
- **Option 4: All of these**:
- Since only Dinoflagellates exhibit mesokaryotic organization, this option is also incorrect.

4. **Conclusion**:
- Based on the analysis of the options, the correct answer is **Dinoflagellates**, as they are the only group among the options that possess mesokaryotic organization.

### Final Answer:
**Dinoflagellates**