Ankheg

These large, insect-like creatures burrow through the ground to surprise prey, which they then snatch in their massive mandibles. The spit of an Ankheg is an extremely corrosive acid that can dissolve flesh, leather, and even steel. Their hide is made from an incredibly tough chitin, which could theoretically make fairly effective plate-armor, although how one would smith it is best left to someone with more experience than the author.