What are the differences among fish skeletal structures, most primitive and more advanced?

Answer

There are three different fish structure types: jawless fish, cartilaginous fish, and bony fish. The first fish, hagfishes, appeared over 2 billion years ago and has no jaw bones. Sharks fall into the second group and all other fish fall into the third group.
Q&A Related to "What are the differences among fish skeletal..."
Primitive fish (class Chondrichthyes) will have a cartilagenous skeleton. More modern species (class Osteichthyes) will have a bony skeleton.
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There are many differences in the skeletal structures of fish from the most primitive to the more advanced types, such as the bony plates on the head of the shark ...
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