It seems sort of counter-intuitive that a spider that builds itself a little fort/trap would be on the side more closely resembling the first spiders, to me at least.  It seems so evolved!  It makes sense that they survived, though.  On the flip side, they’re actually the only family of spiders left in their suborder, Mesothelae.  Arthrolycosidae and Arthromygalidae are both extinct.  Liphistiidae, which is where the trapdoor spider belongs, is the only one left.

What’s sort of neat about the Attercopus fimbriunguis is that it also resembles the scorpion, as it has a similar tail.  I bet the thing was pretty freaky.  Though it’s probably needless to say, the trapdoor spider is also thought to be the most closely related to scorpions of all the spiders.  The earliest scorpions were around 430 millions years ago or so.