To me the whole Fifield thing was that first he was burnt by the Hammerpede acid blood, then he got the black goo which gave him the strength to heal a little bit, not leaving just the skull.... but at the same time morphing him into a more aggresive and resistant creature, maybe the same thing happened to the worms.
I'm also thinking that the black goo spilling from the vases doesn't have the same effect or maybe is not the same stuff that David gives Holloway to drink.......... but since he was burnt by Vickers we´ll never know what really happens to him was he really morphing or getting dissolved like the sacrifice engineer