Bilaterally symmetrical animals
INFRAPHYLUM: Gnathostomes
Jawed vertebrates are grouped into an infraphylum called gnathostomata.
Gnathostomes developed the first adaptive immune system.
An adaptive immune system differs from innate immune system in that it develops the ability to respond differently to different and specific threats from germs and infection. The innate immune system simply reacts to all threats in the same manner.
It is probably fair to assume that gnathostomes first appeared on Earth around 465 million years ago.
Two notable classes within the gnathostomata are the chondrichthyes and the placodermi.
Chondrichthyes are fish with cartilage skeletons. The most well known of these fish is the shark.
Placodermi are an extinct type of fish which were known to have armoured heads and necks. They were not all necessarily scaled fish which is common of all chondrichthyes.
All other jawed vertebrates are referred to as teleostomes.
Teleostomes developed a hard flap to protect their gills. Teleostomes use oxygen for respiration, but also used it for buoyancy when it was wholly aquatic. The oxygen was stored in a gas bladder which has evolved into lungs in non aquatic teleostomes.
Teleostomi contains all amphibians, reptiles, birds and mammals.
Humans are teleostomes.
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Gnathostomes who have developed gas bladders or lungs. |
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CHONDRICHTHYES Fish with cartilage skeletons |
PLACODERMI Extinct fish with articulated armoured head and thorax. |
