The Skinless Ones
Little to nothing is known about these aliens. Its rumored they can wear the skins of other species and are used as infiltrators. We have only encounted one speces like them and so far command is not convinced that they are skinless ones and not just cloned humans. If the rumors are true then they should be able to walk around in th skin of any homosapien species and possibly any species. However right now we are not willing to accept that.
Update: The skinless ones are real. They have taken on the appearance of humans and took over The Spirit of Fire and attempted to engage The Sanctuary. Of course they lost but now we have 100k more people and the possibility of more skin walkers among us. Right now waht we do know about them is that thier skin spoofs sensors to appear human, but thier internal organs and other things are not the same. Current priority is to discoever a way to isolate and eliminate the threat they represent. Right now there is no data on thier independent technology or culture.