Which of the following is a common feature of Ascidia , pristis , Hyla and Calotes ?

Options

A. Skeleton made up of cartilage and bone
B. Solid , dorsal and double nerve cord
C. Three chambered heart with closed circulatory system
D. Paired pharyngeal gill slits at least in embryonic stage

Answer

To determine the common feature of Ascidia, Pristis, Hyla, and Calotes, we can analyze each organism and their characteristics:

### Step 1: Identify the Organisms
- **Ascidia**: A marine invertebrate, commonly known as sea squirt, classified as a urochordate.
- **Pristis**: A genus of cartilaginous fish, commonly known as sawfish.
- **Hyla**: A genus of frogs, which are amphibians.
- **Calotes**: A genus of lizards, which are reptiles.

### Step 2: Classify the Organisms
All four organisms belong to the phylum **Chordata**. This phylum is characterized by certain features during some stage of their life cycle.

### Step 3: Analyze the Options
1. **Skeleton made up of cartilage and bone**:
- Incorrect. While Pristis has a skeleton made of cartilage, Ascidia does not have a skeleton, and Hyla and Calotes have bones.

2. **Solid dorsal double nerve cord**:
- Incorrect. Chordates have a hollow dorsal nerve cord, not a solid one.

3. **Three-chambered heart with a closed circulatory system**:
- Incorrect. Pristis has a two-chambered heart, while Hyla and Calotes have three-chambered hearts. Thus, this option does not apply to all.

4. **Paired pharyngeal gill slits at least in embryonic states**:
- Correct. All chordates, including Ascidia, Pristis, Hyla, and Calotes, exhibit paired pharyngeal gill slits during their embryonic development.

### Conclusion
The common feature among Ascidia, Pristis, Hyla, and Calotes is **paired pharyngeal gill slits at least in embryonic states**. Therefore, the correct answer is **Option 4**.

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