Spiders! Or, well, Cave Spiders! We have green oozes, we have boreworms, we have bats, but wheres the spideys? Our eight legged friends? They keep those pesky bugs from taking over the world, so they need a spot of honor!
And I'm not just talking tiny spiders... I'm talking true Giant Cave Spiders, DF style! The bigger, the better!
I would say they'd be around the size of a cow or so, and that's not including their sexy leg span! They would be a rather strong one to fight, but rather rare, though perhaps a tad more common then the boreworms but much less common than the oozes.
They could give their own meat, perhaps a dex/will, as with as many legs as that it would take some will to fight!
As a curio, perhaps their fearsome fangs or wonderful legs? Instead of bones, because spiders don't have bones, they would give a chitin, that could also act as bone but have some items tied to them, such as perhaps a footwear of some sort, for the irony 
I would offer the idea of different types, but I understand the problem of making things like this, the anims might be a nightmare! (Figuratively AND literally!
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