The animal who possess notochord throughout life is
Or
Which of the following animals is not a vertebrate

Options

A. Fish
B. Amphixus
C. Snakes
D. Birds

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks for an animal that possesses a notochord throughout its life or identifies an animal that is not a vertebrate.

2. **Defining Notochord**: The notochord is a flexible rod-like structure that provides support and is a characteristic feature of the phylum Chordata. In many vertebrates, the notochord is replaced by the vertebral column during development.

3. **Identifying the Options**: The options given are:
- Fish
- Amphioxus
- Snakes
- Birds

4. **Analyzing Each Option**:
- **Fish**: Fish are vertebrates. They have a vertebral column that replaces the notochord during development.
- **Amphioxus**: Amphioxus (also known as lancelets) belongs to the subphylum Cephalochordata. It retains the notochord throughout its life and does not have a vertebral column, making it an invertebrate.
- **Snakes**: Snakes are vertebrates, and like other vertebrates, their notochord is replaced by a vertebral column.
- **Birds**: Birds are also vertebrates, and their notochord is replaced by a vertebral column during development.

5. **Conclusion**: The only animal from the options that retains the notochord throughout its life and is not a vertebrate is **Amphioxus**.

### Final Answer: Amphioxus

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