Which of the following character is unique to Tusk - shell ?

Options

A. Water vascular system
B. Head , muscular foot and visceral hump
C. Radial symmetry
D. Choanocytes

Answer

To determine the unique character of Tusk Shell (also known as Dentalium), we need to analyze the provided options one by one.

### Step-by-Step Solution:

1. **Identify the Options**: The question provides several options to choose from regarding the unique character of Tusk Shell.

2. **Evaluate Option 1: Water Vascular System**:
- The water vascular system is a characteristic of echinoderms, such as sea stars and sea urchins.
- Since Tusk Shells are mollusks, this option does not apply to them.
- **Conclusion**: This option is incorrect.

**Hint**: Remember that the water vascular system is specific to echinoderms, not mollusks.

3. **Evaluate Option 2: Head, Muscular Foot, and Visceral Hump**:
- Tusk Shells possess a head, a muscular foot for locomotion, and a visceral hump that contains the internal organs.
- These features are indeed characteristic of Tusk Shells and are not found in other mollusks in the same combination.
- **Conclusion**: This option is correct.

**Hint**: Look for features that are specific to the morphology of Tusk Shells.

4. **Evaluate Option 3: Radial Symmetry**:
- Tusk Shells exhibit bilateral symmetry, not radial symmetry.
- Radial symmetry is typically found in organisms like jellyfish and some echinoderms.
- **Conclusion**: This option is incorrect.

**Hint**: Recall that Tusk Shells are elongated and have a bilateral shape.

5. **Evaluate Option 4: Quinocide**:
- Quinocide is a term related to sponges, specifically referring to the filtering mechanism.
- Tusk Shells do not possess this feature.
- **Conclusion**: This option is incorrect.

**Hint**: Quinocide is associated with sponges, not Tusk Shells.

### Final Answer:
The unique character of Tusk Shell is **Option 2: Head, Muscular Foot, and Visceral Hump**.