Water current is maintained in Herdmania by

Options

A. Rhythmic contractions of tunic
B. Opening and closing of atrial and branchial apertures
C. Constraction of incurrent siphon
D. Cilia bordering gill slits

Answer

### Step-by-Step Solution

1. **Understanding Herdmania**: Herdmania, commonly known as a sea squirt, is a member of the subphylum Urochordata within the phylum Chordata. It is a marine organism that has a sedentary lifestyle.

2. **Water Current Function**: In Herdmania, water current is essential for feeding and respiration. The organism filters food particles from the water that flows through its body.

3. **Role of Cilia**: The primary mechanism for maintaining water current in Herdmania is through the action of cilia. These tiny hair-like structures are located at the borders of the gill slits (or gill openings) of the organism.

4. **Ciliary Movement**: The cilia beat in a coordinated manner, creating a flow of water. This movement helps to draw water into the body through the incurrent siphon and out through the excurrent siphon, effectively maintaining a continuous water current.

5. **Elimination of Other Options**:
- **Muscular Contraction of Tunic**: This does not play a significant role in water current maintenance in Herdmania.
- **Opening and Closing of Atrial and Branchial Apertures**: While these apertures are present, they do not actively control water flow as cilia do.
- **Construction of the Incurrent Siphon**: This is not a mechanism for water current maintenance in Herdmania.

6. **Conclusion**: The correct answer to the question is that water current in Herdmania is maintained by the cilia located at the borders of the gill slits.

### Final Answer
Water current in Herdmania is maintained by cilia at the borders of the gill slits.

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