All chordates posses the following features except

Options

A. Dorsal hollow nerve cord
B. Pharyngeal gill slits
C. Notochord
D. Amnion

Answer

To solve the question "All chordates possess the following features except," we need to identify which feature is not common to all chordates. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Common Features of Chordates
Chordates are defined by several key characteristics:
- **Notochord**: A flexible rod-like structure that provides support.
- **Dorsal Hollow Nerve Cord**: A nerve cord that runs along the back of the organism.
- **Pharyngeal Slits**: Openings in the pharynx that can develop into gill structures.
- **Ventral Heart**: The heart is located on the ventral side of the organism.
- **Postanal Tail**: An extension of the body past the anal opening.

### Step 2: Analyze the Options
The question implies that there are options provided, and we need to determine which one does not belong to all chordates. The features mentioned above are typical of chordates.

### Step 3: Identify the Exception
Among the features listed, the **amnion** is an embryonic structure that is not present in all chordates. It is found in certain groups such as mammals, birds, and reptiles, but not in all chordates, particularly in subphyla like **urochordates** and **cephalochordates**.

### Step 4: Conclusion
Since the amnion is not a characteristic feature of all chordates, it is the correct answer to the question. Therefore, the answer to the question is the **amnion**.

### Final Answer
The feature that is not present in all chordates is the **amnion**.

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