Question

Jaws are absent in:

• A. (i), (iv)
• B. (ii), (iv)
• C. (i), (ii)
• D. (iii), (iv)

Answer 1

The correct option is B

(ii), (iv)

The correct option is B

Explanation of the correct option:

Petromyzon:

1. It is classified as an Urochordate.
2. It is also called sea lamprey and doesn't have bony teeth and jaws.

Myxine:

1. It is considered a cephalochordate in which jaws are absent and notochord is present from the brain to the tail.
2. Therefore due to the absence of jaws, they are both called Protochordates.

Explanation of the incorrect option:

Option A:

Balanoglossus:

1. It shows half vertebrate and half invertebrate characters.
2. Probosis, collar, and trunk are found.
3. The mouth is present in the proboscis, where the partial formation of jaws is found, which helps to intake the food.

In Myxine, jaws are absent and they are called protochordates because of the absence of jaws.

Option C:

1. In Balanoglossus, partial formation of jaws is found, which helps to intake the food.
2. In Myxine, jaws are absent and notochord is present from the brain to the tail.

Option D:

Vertebrates:

1. Composed of the upper and lower jaw.
2. Jaws are bony and cartilaginous and oppose each other vertically.

In Petromyzon, bony teeth and jaws are absent.

Final answer: Jaws are absent in Myxine and Petromyzon.