Look, as much as I was going to just let this trainwreck be, since watching this get ludicrously derailed rather proves the point of discussion organization I had made earlier, there's a simple answer to this:
Toady made a [MUNDANE] token. Any creature that is scientifically possible has one. Any creature that does not have a [MUNDANE] token is considered "magic" by Toady.
GoblinCookie entered this thread saying that a walking, semi-sentient pile of rocks was totally the same thing as a car, and that wild leap of 'logic' proves it's not magic. It's clear GoblinCookie is making irrational arguments. Arguing rational arguments against someone making an irrational argument will never persuade them, as evidenced by how GoblinCookie simply does not recognize the premise of the rational argument being put forth by Expwnent.
As for this:
Well as long as there's oxygen or a similar corrosive agent involved, chemotrophs could feed off of the rock itself by breaking down the surface they're growing on. Assuming this happens on an open wall/ceiling, that could lead to small piles of waste-soil on the cavern floor around such colonies that could then support additional fungal niches.
As already discussed in the previous threads ad nauseum, yes, that exists, but it's nowhere near capable of generating enough energy to be put into the ecosystem for licking caustic slime off of rocks to plausibly sustain a small city, much less the biodiversity of the cavern system. Nor is there enough decaying material from the surface to support that life, nor does the magma reach high enough for the upper caverns to support life, nor do cosmic rays or any other outlandish energy source (yes, that was proposed) make for any plausible substitute for a magical power source. Just because a process is "possible" does not make something believable or rational if you completely ignore scale. An ordinary human can lift things with their hand, but then saying that it's totally the same thing if a supposedly ordinary human lifts a skyscraper off its foundations (
without tunneling themselves through the earth trying, no less,) with one hand as when they lift leaf is pretending impossibility of scale is somehow "forgivable" when impossibility of concept is not. Lifting a skyscraper may be conceptually possible, but for a human to do so is no less "fantastic" than a wizard using telekinesis to accomplish the same feat.
For that matter, the very
existence of those world-spanning caverns is clearly unnatural. Real caverns are formed almost exclusively in limestone, (which is soluble in acidic water,) or ice near arctic volcanoes. There are no giant, horizontal caverns throughout a granite layer.
The caverns, and everything in them shy of bats, cave swallows, and other [MUNDANE] cave creatures are fantasy. Period. That's why they are marked as such.