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 solve the question "Which of the following character is unique to Tusk-shell?", we will analyze the characteristics of Tusk-shells (also known as Tusk shells or Dentalium) and compare them with the options provided.

### Step-by-Step Solution:

1. **Identify the Organism**: Tusk shells belong to the class Scaphopoda within the phylum Mollusca. They are also referred to as tooth shells due to their conical and slightly curved shape.

2. **Understand the Characteristics of Tusk Shells**:
- Tusk shells have a conical, elongated shell that is open at both ends.
- They possess a head, muscular foot, and a visceral hump.
- They do not exhibit radial symmetry; instead, they have bilateral symmetry.

3. **Evaluate the Options**:
- **Option 1: Vesicular system** - This is incorrect as the vesicular system is characteristic of echinoderms like sea stars and sea urchins, not Tusk shells.
- **Option 2: Head, muscular foot, and visceral hump** - This is correct as these features are indeed present in Tusk shells.
- **Option 3: Radial symmetry** - This is incorrect because Tusk shells exhibit bilateral symmetry, not radial symmetry.
- **Option 4: Kwanocytes** - This is incorrect as Kwanocytes are unique to sponges, not Tusk shells.

4. **Conclusion**: The unique characteristic of Tusk shells is the presence of a head, muscular foot, and visceral hump.

### Final Answer:
The characteristic unique to Tusk shells is the **head, muscular foot, and visceral hump**.