What are the most primitive fish?

The most primitive fish are typically represented by the jawless fish known as agnathans, which include species like lampreys and hagfish. These fish have a simple body structure and lack jaws, fins, and paired appendages, differentiating them from more advanced fish. They are considered some of the earliest vertebrates, having existed for hundreds of millions of years, providing insights into the evolution of more complex fish and vertebrates. Their unique characteristics make them a significant focus in studies of vertebrate evolution.