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 classification of two spider families, Phyxelididae and Titanoecidae, has been debated by researchers.  Some studies suggest these families are closely related and form a clade, but other studies have placed Titanoecidae outside the RTA clade while Phyxelididae is within it.