Why is ammocoete special?

Answer 1

Ammocoetes are unique because they have many features in common with true vertebrates, but retain many primitive characteristics of their ancestors.

These are the larval phase of all lamprey species, and are of high importance to many evolutionary biologists as they are more commonly available then the other group of jawless fishes (i.e. hagfish). They are also of interest to biologists because no other living group of fishes exhibit a life history similar to lampreys. Finally the larval stage of sea lamprey is also the target of large scale and yearly eradication efforts throughout all of the Great Lakes in the United States and Canada.