Hey CTD.

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Shouldn't it be that no skin information is hereditary then?
No, because hereditary traits can affect how skin looks and behaves in the sun - variations is color (including mottled), variations in susceptibility to burn vs tan, as well as texture can be due to genes, and thus the results of those genetic traits on the developed organism are susceptible to selection with different results in different ecologies. They can also play a role in sexual selection. Hair the same.

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Still doesn't explain how any creature can have skin... Tough riddle there.
All skin is, basically, is a colony of cells, not that different from sponges.

http://ebiomedia.com/prod/BOsponges.html
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Sponges are clearly the simplest of the conspicuous animal phyla, and thus are important subjects for considering the evolution of the animals. Recent studies using the tools of molecular genetics indicate that the animal kingdom evolved only once, and that the Phylum Porifera is at the base of the animal tree of life. In this sense, sponges represent a key group for understanding relationships among the other animal phyla.
There are some primitive sponges that you can put through a screen, breaking them up into small bits, and they will reassemble into a colony.

Enjoy.