The taxon contains two families of spiders, Phyxelididae and Titanoecidae. Although some phylogenetic studies have shown these two families to form a clade, other studies have not, placing Titanoecidae outside the RTA clade while Phyxelididae is placed inside it.
The taxonomic group includes two spider families: Phyxelididae and Titanoecidae.  Some research suggests these families are closely related, forming a single evolutionary lineage (a clade), but other studies suggest they are not closely related and that Titanoecidae is separate from the RTA clade, while Phyxelididae belongs to it.