Contractile structure of nematoblast is

Options

A. Lasso
B. Cnidocil
C. Tube
D. Refractive rods

Answer

To answer the question regarding the contractile structure of nematoblast, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nematoblasts**:
- Nematoblasts are specialized cells found in cnidarians (such as jellyfish, corals, and sea anemones) that contain nematocysts, which are stinging structures.

2. **Identifying the Components of Nematoblasts**:
- Each nematoblast contains a capsule that houses a coiled thread-like structure. This thread is capable of being expelled rapidly when triggered.

3. **Recognizing the Contractile Structure**:
- The contractile structure within the nematoblast is known as the "lasso." This structure is responsible for the rapid expulsion of the thread when the nematoblast is activated.

4. **Function of the Lasso**:
- The lasso serves a defensive function. When the cnidarian senses danger, the lasso contracts, ejecting the thread that can inject toxins into potential threats, effectively paralyzing them.

5. **Conclusion**:
- Therefore, the correct answer to the question is that the contractile structure of the nematoblast is the "lasso."

### Final Answer:
The contractile structure of nematoblast is the **lasso**.

---