Microscopic aquatic organisms lacking locomotory ability and
drifting with water current are

Options

A. Pleuston
B. Nekton
C. Plankton
D. Seston

Answer

To solve the question "Microscopic aquatic organisms lacking locomotory ability and drifting with water current are," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the type of microscopic aquatic organisms that cannot move independently and instead drift with the water current.

2. **Analyze the Options**:
- **Pleustron**: These organisms live at the air-water interface but are not specifically defined by their inability to move with currents.
- **Nekton**: This group includes organisms that can swim independently against currents, which does not fit the description of lacking locomotory ability.
- **Plankton**: This group consists of organisms that are suspended in water and lack the ability to swim against currents. They drift with the water currents.
- **Cestron**: This term is not commonly used in biological classifications related to aquatic organisms and does not fit the description provided.

3. **Identify the Correct Option**: Among the options, **Plankton** is the only group that fits the description of being microscopic, lacking locomotory ability, and drifting with water currents.

4. **Conclusion**: Therefore, the correct answer to the question is **Plankton**.

### Final Answer:
The microscopic aquatic organisms lacking locomotory ability and drifting with water current are **Plankton**.

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