Melanin is a pigment that is produced by cells known as melanocytes in the skin of most animals, including humans. ...
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.
You need to be a bit more specific!!
