a). On March 17th 2012, Prometheus - Imax 3D Incredible Trailer we see a quick shot of the white tale of a creature vanishing into the arm of the suit of one of the characters in the movie, we have no idea what this is supposed to represent. In the in the March 18th " Prometheus - New International Extented Trailer" see the same shot a fragment of a second longer.
b). In the Prometheus International extended launch trailer released on April 30th, 2012 we are presented with the creature, first of all it's seen to be slithering through the small stream of liquid seen running through the ampule chamber it first looks like a sprouting plant and its head unfolds to present a shape, it almost resembles a pelvic girdle and at the centre of this things head is an opening like an anal sphincter. It's head is raised before the explorer like that of a cobra.
c). The thing latches onto the arm of the human explorer. Perhaps he feels that this he has enough hand protection from his suit, but this creature begins to wrapping the side extensions of its head around the wrist and somehow enters the arm of his suit.
d). On the 11th of May, Amazon.com reveal the tracklistings of the soundtrack for Prometheus, there is one track called Hammerpede, is this the name of this strange creature despite the lack of hammer shaped feet.
e). In TV trailer made available on the internet on 15th May 2012, we see the creature having moved through the suit's arm enters the helmet and forces itself down the victims throat.
f). In the book "Prometheus , the art of the film" released at the beginning of June 2012, it is finally revealed that this creature is indeed the Hammerpede.