"Of all Terrinoth's greatest dangers, its giant arachnids are the absolute worst. The best way to deal with them is to set the surrounding area alight. It's the only way to be sure!" - Brightcarver's Bestiary
Arachyura are giant mutated arachnids found very deep underground. There is an infestation of the terrible things at the lost ruins of Sudanya.
It takes many, many years in the deepest of underground caves for a simple spider to mutate to such an absurd size, but thus far their reclusive nature has typically led them to be seldom encountered. Why these terrible creatures have emerged from their dark hovels is unknown, but it bodes ill tidings for all the surface dwelling peoples.
References
- Descent: Journeys in the Dark (Second Edition): Labyrinth of Ruin