Characteristic of rotifers is

Options

A. Small size
B. Ring of cilia
C. Multicellular nature
D. All the above.

Answer

### Step-by-Step Solution

1. **Definition of Rotifers**:
- Rotifers are microscopic, free-living organisms that belong to the phylum Rotifera. They are often found in freshwater environments.

2. **Body Structure**:
- Rotifers are pseudocoelomates, meaning they have a body cavity that is not completely lined by mesoderm. They are multicellular organisms, which places them in the category of metazoans.

3. **Digestive System**:
- One of the key characteristics of rotifers is that they possess a complete digestive tract. This means their digestive system has two openings: a mouth and an anus. The digestive process starts at the mouth and ends at the anus.

4. **Organ Systems**:
- Rotifers have specialized organ systems, which allow them to perform various functions necessary for survival. This includes their digestive system and reproductive organs.

5. **Reproductive Features**:
- The gonads in rotifers are paired in both sexes, indicating that they have distinct male and female reproductive organs. Males exhibit sexual dimorphism, meaning they have different physical characteristics compared to females.

6. **Body Shape**:
- Rotifers typically have an elongated body shape. They also possess a structure known as the corona, which is a ring of cilia around their mouth. This cilia helps in locomotion and feeding, creating a wheel-like motion.

7. **Conclusion**:
- Based on the characteristics discussed, we can conclude that rotifers are small-sized, multicellular organisms with a complete digestive tract and a ring of cilia. Therefore, the correct answer to the question about the characteristics of rotifers is "all of the above."