There are not many synonyms for the word "Petromyzoniformes" as it is a scientific term used to describe an order of jawless fish that are commonly known as lampreys. However, there are a few words that can be used in place of Petromyzoniformes, including "lamprey-like fish," "jawless vertebrates," and "agnathan fish." Lampreys are ancient fish that have been around for more than 360 million years, and they are known for their unique feeding habits and bizarre appearance. Although there are not many synonyms for Petromyzoniformes, these animals are certainly fascinating creatures that are worth learning more about.