It's something called a Seeker (most likely a lesser daedra serving Hermaeus Mora). The name was revealed by the filename on one of the 12 released screenshots
(it should have a section on Dragonborn - if you don't see it, change the language to english).
Originally Posted by Rake21
So, as a guy who never played Morrowind, I just want to make sure I understand this Corpus thing.
It's basically a disease that drives you nuts, connects you to an insane god-like entity, and warps your body into a twisted abomination. Is that about right?
Cause that's awesome.
It also makes you immortal (as in: can't die of old age), though most victims die due to various accidents. Though we should use the past tense - after the events of Morrowind it lost most of it's potential.