Heterocyst is a specialised structure in some monerans. It cannot be a feature of

Options

A. Filamentous cyanobacteria
B. Nostoc and Anabaena
C. Oxyphotobacteria
D. Chemosynthetic autotroph

Answer

To solve the question regarding the presence of heterocysts in monerans, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Heterocysts**:
- Heterocysts are specialized cells found in certain types of bacteria, particularly in cyanobacteria. They are involved in nitrogen fixation, a process where atmospheric nitrogen is converted into a form usable by plants.

2. **Identifying Organisms with Heterocysts**:
- Heterocysts are primarily found in filamentous cyanobacteria such as Nostoc and Anabaena. These organisms are capable of photosynthesis and are known to fix nitrogen.

3. **Differentiating Types of Bacteria**:
- There are various types of bacteria, including:
- **Cyanobacteria**: These are photosynthetic and can have heterocysts.
- **Chemoautotrophs**: These bacteria obtain energy by oxidizing inorganic substances and do not rely on photosynthesis or nitrogen fixation in the same way.

4. **Conclusion**:
- Since heterocysts are associated with nitrogen-fixing cyanobacteria and not with chemoautotrophic bacteria, we can conclude that heterocysts cannot be a feature of chemoautotrophic bacteria.

### Answer:
Heterocyst is a specialized structure in some monerans, but it cannot be a feature of **chemoautotrophic bacteria**.