What is correct?

Options

A. Archaeopteryx is connecting link between Aves and Mammalia
B. Sea Horse is connecting link between fish and horse
C. Duck Billed Platypus is connecting link between reptiles and mammals
D. Hydra is connecting link between protozoa and metazoa

Answer

To determine which statement is correct regarding the connecting links between different groups of animals, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Concept of Connecting Links**:
- A connecting link refers to an organism that exhibits characteristics of two different groups, showing evolutionary relationships between them.

2. **Analyzing Each Option**:
- **Option 1**: "Archaeopteryx is a connecting link between apes and mammals."
- **Analysis**: Archaeopteryx is actually a connecting link between reptiles and birds, not apes and mammals. This statement is **incorrect**.

- **Option 2**: "Seahorse is a connecting link between fish and horse."
- **Analysis**: Seahorses are fish and do not have characteristics that link them to horses. This statement is **incorrect**.

- **Option 3**: "Duck-billed platypus is a connecting link between reptiles and mammals."
- **Analysis**: The duck-billed platypus exhibits features of both reptiles (like laying eggs) and mammals (like producing milk). This statement is **correct**.

- **Option 4**: "Hydra is a connecting link between protozoa and metazoa."
- **Analysis**: Hydra is a simple multicellular organism and does not serve as a connecting link between protozoa (single-celled organisms) and metazoa (multicellular organisms). This statement is **incorrect**.

3. **Conclusion**:
- After analyzing all options, the only correct statement is **Option 3**: "Duck-billed platypus is a connecting link between reptiles and mammals."

### Final Answer:
The correct statement is: **Duck-billed platypus is a connecting link between reptiles and mammals.**

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