You can Change the Name into Idmonarachne brasieri and add some bioluminescence Regions like other Aberration Creatures.
https://en.wikipedia.org/wiki/Idmonarachne
No matter about the Size the REAL Rhyniognatha was just like 1mm and not 2m.
Megarachne wasn't a spider, since 2005 it's an Eurypterid Species.
https://www.nationalgeographic.com/science/article/megarachne-the-giant-spider-that-wasnt
https://en.wikipedia.org/wiki/Megarachne