I wouldn't take any of the images in that poster as being in Covenant, its a mash up of various different styles and - it looks to me - some existing alien poses from different movies redrawn into a poster. The new alien from the trailer is there at the bottom, wiry and muscled as in the trailer and without biomechanical elements, but others do have. One looks like a traditional straight on head pose from alien, one looks like the well known alien head with much elongated jaw and teeth from the (?) avp movies, etc.
I'm not complaining, I think it's excellent, just don't get your hopes up for those different aliens that can be found in the image, is all I'm saying :-)
The central one looks like Alien 3 to me, redrawn with a different body.
