The funny thing is that there are colonies of archaeoprotozoans that sparsely populate the fractured shale that underlies the majority of the world's aquifers. They died back during the Silurian period, the temperatures of the aquifers having dropped to non-optimal levels. As the aquifers start absorbing surface calories, the environment may become more hospitable to these colonies.
Now I know what you're thinking: "Zombies. Hordes of ravenous zombies, feasting on the flesh of the living." That's what I thought too, having seen enough educational television to know what's what. But further research (from assumed principles, not the empirical work that passes for science these days) shows that the colonies would likely not interact with topside biology, so the West-Guimard reaction would not occur.
At least not initially. It turns out that in the process of drilling geothermal wells bits of human DNA can be introduced into the aquifers, which can in turn be incorporated into the pRNA of the colonies. I'll skip ahead here, since I'm addressing an educated audience. Thus:
. . . upon achieving the requisite level of connectivity, the sheets of protozoan tissue will have achieved sentience. This coupled with the higher levels of proteins in the aquifer (resulting in low impedance to chemo-electrical signals) provides an ideal setting for a networked intelligence. The reflective and amplifying characteristics of certain aquifer geometries may very well result in "spillage" or "leaking" of these signals to the surface. . . .
Again, I'll skip ahead:
. . . blasphemous piercing of the chthonic vaults of the Old Ones, minds torn asunder by those unholy emanations, infants twisted in the womb to shapes not seen on this planet since the moon coalesced from the Great Ring, rifts in the mantle of the Earth spilling forth long-subsumed telluric currents, vomiting forth armies girded not in leather or steel but in the horn-like carapaces they were born with -- or designed to bear by something still more ancient and unutterably evil. . . .
You get the idea.