Sensory structure of a cnidoblast is

Options

A. Cnidocil
B. Refractile rods
C. Myonemes
D. Operculum.

Answer

To solve the question regarding the sensory structure of a cnidoblast, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terminology**:
- A cnidoblast (or cnidocyte) is a specialized cell found in cnidarians (like jellyfish, corals, and sea anemones) that contains a stinging structure called a nematocyst.

2. **Identify the Options**:
- The options provided are:
- A) Needle cell
- B) Refractile rods
- C) Myonemes
- D) Operculum

3. **Analyze Each Option**:
- **Needle cell**: This term is often used interchangeably with cnidocyte, which is involved in sensory functions and the discharge of nematocysts.
- **Refractile rods**: These are not primarily sensory structures; they are involved in light refraction.
- **Myonemes**: These are contractile elements in some cells and are not related to sensory functions in cnidoblasts.
- **Operculum**: This is a part of the nematocyst that opens to release the stinging thread but is not a sensory structure itself.

4. **Determine the Correct Answer**:
- The correct answer is **Needle cell** (or cnidocyte), as it serves as a mechano- and chemoreceptor that can trigger the discharge of the nematocyst.

5. **Conclusion**:
- Therefore, the sensory structure of a cnidoblast is the **Needle cell**.