I was just reading through this thread, and it occurs to me that what David did, may have been skin deep after all. In the movies, it is clear that he was playing around with insects. Perhaps the single major point of difference between insects and most animals is that their bone structure is on the outside. So David could have introduced the external shell to the basic alien species which he discovered. There is no way of knowing what the skin texture was like on the creatures in the mural. It could have been like the noemorph. If David's work was skin deep in this way, then it would be literal, but by no means superficial. And yet clearly he would be as mistaken about where credit is due for creation, as he was about the poem in Covenant.