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 will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding the Organisms**:
- **Ascidia**: A marine invertebrate belonging to the subphylum Tunicata (or Urochordata).
- **Pristis**: A genus of rays commonly known as sawfish, which are cartilaginous fish.
- **Hyla**: A genus of tree frogs, which are amphibians.
- **Calotes**: A genus of lizards, which are reptiles.

2. **Analyzing the Options**:
- **Option 1: Skeleton made up of cartilage and bone**:
- This is incorrect as Ascidia does not have a skeleton made of cartilage or bone; it lacks a hard skeleton. Pristis has a cartilaginous skeleton, while Hyla and Calotes have bony skeletons. Therefore, this option does not apply to all four organisms.

- **Option 2: Solid, dorsal, and double nerve cord**:
- This option is also incorrect. Ascidia does not have a solid dorsal nerve cord; it has a simple nerve net. The solid dorsal nerve cord is characteristic of vertebrates, but not all the listed organisms possess this feature. Thus, this option is not common to all.

- **Option 3: Three-chambered heart with a closed circulatory system**:
- This option is incorrect as well. While Hyla and Calotes have three-chambered hearts, Ascidia does not have a closed circulatory system, and Pristis has a different heart structure. Therefore, this option does not apply to all.

- **Option 4: Paired pharyngeal gill slits at least in the embryonic stage**:
- This is the correct option. All four organisms exhibit paired pharyngeal gill slits during their embryonic development. This feature is a characteristic of the phylum Chordata, which includes all four organisms.

3. **Conclusion**:
- The common feature among Ascidia, Pristis, Hyla, and Calotes is **paired pharyngeal gill slits at least in the embryonic stage**.

### Final Answer:
The correct answer is **Option 4: Paired pharyngeal gill slits at least in the embryonic stage**.