Jawless Entelognathus primordialis is the most ancient fish.
The Lamprey is an eel-like shaped, jawless fish of the order Petromyzontiformes.
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Bony fishHag fishLamprey(both of these are known as the jawless fish)Sharks and rays(both of these are known as cartilaginous fish)Lob-finned fishThis is a very simplified classification of something that is very complex. To see the full tree, try WikiSpieces.
They were jawless fish that lived during the Paleozoic era Stunningly some of our oldest ancestors came from ostracoderms!
They don't have a central nervous system. Just 2 ganglia.
Agnathans are the jawless fish. They are usually fairly small (a few centimeters in length.) They consist of lancelets and tunicates. They have a notochord which is like a backbone, but it is more flexible than bone. Tunicates are enveloped by a tough tunic around their bodies. Other than that, they have no other bones.
intrinsic eye muscles are controlled by the autonomic nervous system
central
Both jawless fish and cartilaginous fish have skeletons composed of cartilage and distinct brains. Also, some cartilaginous fish don't have scales, and all jawless fish don't have scales. Cartilaginous fish, however, have jaws, paired appendages, and a kind of vertebrae. Jawless fish do not have jaws, paired appendages, and often are without vertebrae.
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The nervous system is made of these kinds of cells... -smooth muscle cells -nerve cells