Answer:
gills
Explanation: A fish without a jaw was the first vertebrate to evolve. These fish used filtration to capture their food and sucked water and debris from the sea through their mouths and then released the water and trash through their gills. Some features are as follows:
1. They have a notocorda that serves as support through the back of the fish.
2. Gill bags. These organs are responsible for filtering the oxygen in the water.
3. A pineal eye that is sensitive to light
4. A cartilaginous skeleton