The unique characteristic of annelida is
(a) Coelom
(b) Nephridia
(c) Hermaprodite
(d) Alimentary canal is complete

Options

A. Coelom
B. Nephridia
C. Hermaprodite
D. Alimentary canal is complete

Answer

To determine the unique characteristic of the phylum Annelida from the given options, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Annelida**:
- Annelida is a large and important phylum that includes segmented worms known as annelids. They exhibit several key characteristics.

2. **Option A: Coelom**:
- Annelids possess a true coelom, which is a body cavity located between the body wall and the gut wall. However, coelom is not unique to annelids as other phyla, such as Mollusca and Arthropoda, also possess a coelom. Therefore, this option is not unique to annelids.

3. **Option B: Nephridia**:
- Nephridia are excretory structures found in annelids that help in the removal of nitrogenous waste. This feature is considered unique to annelids, as other phyla do not possess this specific type of excretory organ. Thus, this option stands out as a unique characteristic of annelids.

4. **Option C: Hermaphrodite**:
- Many annelids are hermaphrodites, meaning they have both male and female reproductive organs. However, hermaphroditism is also found in various other organisms across different phyla, making this characteristic not unique to annelids.

5. **Option D: Alimentary Canal is Complete**:
- Annelids have a complete alimentary canal, which means they have a distinct mouth and anus. However, this feature is also present in many other organisms, including arthropods and chordates. Therefore, this option is not unique to annelids.

### Conclusion:
After analyzing all the options, the unique characteristic of annelids is the presence of **nephridia** (Option B).

### Final Answer:
**(b) Nephridia**

---