The presence of a special sense organ statocyst at the opposite end of mouth that is (aboral end) is the characteristic
1)Cnidarians
2) Platyhelminthes
3) Ctenophora
4) Nematodes

Options

A. Cnidarians
B. Platyhelminthes
C. Ctenophora
D. Nematodes

Explanation

To solve the question regarding the presence of a special sense organ called statocyst at the aboral end (opposite end of the mouth), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the term "statocyst":**
- A statocyst is a specialized sense organ that helps in maintaining balance and orientation in certain organisms. It contains structures called statoliths, which are typically made of calcium carbonate.

2. **Identify the function of the statocyst:**
- The primary function of the statocyst is to assist the organism in sensing its position in the environment, thus aiding in balance and orientation.

3. **Analyze the options provided:**
- **Option 1: Cnidarians** - While they have specialized structures, they do not have statocysts.
- **Option 2: Platyhelminthes** - These flatworms do not possess statocysts.
- **Option 3: Ctenophora** - This phylum is known for having statocysts located at the aboral end, which is crucial for their balance and orientation.
- **Option 4: Nematodes** - Roundworms do not have statocysts.

4. **Conclude based on the analysis:**
- Since the presence of statocysts at the aboral end is a defining characteristic, and the only phylum that possesses this feature is Ctenophora, the correct answer is **Option 3: Ctenophora**.

### Final Answer:
**The correct answer is Option 3: Ctenophora.**

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