Which of the following is a common feature of Amphioxus, frog, fish and crocodile?

Options

A. Skeleton made up of cartiage and bone
B. Pharyngeal gill slits at least in developmental stages
C. Dorsal solid nerve cord
D. Three chambered heart

Answer

To determine the common feature of Amphioxus, frog, fish, and crocodile, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group**:
- All four organisms (Amphioxus, frog, fish, and crocodile) belong to the phylum Chordata. This is the first commonality we can establish.

2. **List Key Characteristics of Chordates**:
- Chordates are characterized by several key features:
- Presence of a notochord
- Paired pharyngeal gill slits
- Dorsal hollow nerve cord

3. **Analyze Each Characteristic**:
- **Notochord**: Present in all chordates during some stage of development, but may be replaced by a vertebral column in adult forms (like frogs, fish, and crocodiles).
- **Paired Pharyngeal Gill Slits**: These are present at least during the developmental stages of all chordates, including Amphioxus, frogs, fish, and crocodiles.
- **Dorsal Hollow Nerve Cord**: This is a defining feature of chordates, but it is hollow, not solid.

4. **Evaluate the Options**:
- Compare the characteristics with the options provided in the question:
- **Skeleton made of cartilage and bone**: Not a common feature.
- **Pharyngeal gill slits**: Present at least in developmental stages for all four organisms, making this option correct.
- **Dorsal solid nerve cord**: Incorrect, as chordates have a dorsal hollow nerve cord.
- **3 chambered heart**: Not common to all; different species have different heart structures.

5. **Conclusion**:
- The common feature among Amphioxus, frog, fish, and crocodile is the presence of paired pharyngeal gill slits at least during their developmental stages.

### Final Answer:
The common feature of Amphioxus, frog, fish, and crocodile is **paired pharyngeal gill slits at least in developmental stages**.

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