<span>One reflex reaction to maintaining homeostasis in the body is shivering. In response to cold temperatures, the muscular system moves our muscles quickly to warm them up as a rapid, short term solution for homeostasis. Another example is the withdrawal reflex, which occurs as a response to pain. Pain receptors activated by the painful stimulus activate the motor neurons in the body, which in turn contract muscles to move parts of your body away from the pain.</span>
I would say that the fishes exhibited the greatest diversity (though the brachiopods also had considerable diversity) and mostly were of the ostracoderms (with a platey or shell-like skin and no jawbone) which exhibited many varieties and also the placoderm which had gills, a jawbone and fins so was developing characteristics of modern fish.
A complex chemistry is most related to maintaining a stable internal environment.
