Circular and suctorial mouth is present in :-

Options

A. Labeo
B. Petromyzon
C. Scoliodon
D. All the above

Answer

To determine which organism has a circular and suctorial mouth, we can analyze the options provided step by step.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which organism possesses a circular and suctorial mouth. This type of mouth is typically adapted for suction feeding.

2. **Analyzing Option 1: Labio**:
- The labio (Labio roita) is known to have pharyngeal teeth located in the dorsolateral wall.
- It does not have a circular or suctorial mouth; instead, it has jaws and palates that are adentulous (without teeth).
- **Conclusion**: This option is incorrect.

3. **Analyzing Option 2: Patromyzon**:
- Patromyzon, which refers to lampreys, is known for having a circular and suctorial mouth.
- Their mouth is adapted for sucking blood from their host, which is characteristic of this group.
- **Conclusion**: This option is correct.

4. **Analyzing Option 3: Squalidon**:
- Squalidon refers to a group of extinct sharks.
- They have a mouth located on the ventral side and are bounded by jaws, which does not fit the description of a circular and suctorial mouth.
- **Conclusion**: This option is incorrect.

5. **Analyzing Option 4: All of the Above**:
- Since we have already determined that only Patromyzon has a circular and suctorial mouth, this option cannot be correct.
- **Conclusion**: This option is incorrect.

### Final Answer:
The correct answer is **Option 2: Patromyzon**.