While the name of Ridley Scott's Prometheus sequel appears to be shifting from Alien: Paradise Lost to Alien: Covenant, one rumor suggests two alien creatures will be doing their best to kill the human protagonists.
According to Scified (via comicbook.com), one creature will be a completely new element that their source claims "is going to be based off of the Original Concept that Alien drew influence from, and this idea is something they had planned with Spaights'[sic] Ultramorph." They also claim it will be transparent "like a jelly fish" and that android miscreant and Peter O'Toole cosplayer David may have a hand in its creation.
An earlier draft of Prometheus by writer Jon Spaihts featured a much larger alien birthed by one of the Engineers, referred to in the script as the Ultramorph:
As always, it could be wishful thinking or ideas already discarded by the director. That Spaihts draft of Prometheus was more of a direct Alien prequel than the eventual film. It is possible this giant "jelly fish" alien will only be realized in concept designs, just like the Ultramorph.
In any event, that Prometheus sequel is scheduled for a May 30th, 2017 release.