This study revises the taxonomy, biology, phylogeny, and biogeography of the basal-most nephilid spider lineage, the Clitaetrinae, with the least known nephilid genus Clitaetra. The five previously known species are redescribed: Clitaetra clathrata Simon from western Africa, C. simoni Benoit from central Africa, C. episinoides Simon from the Comoro Islands and Mayotte, C. perroti Simon from Madagascar, and C. thisbe Simon from Sri Lanka with first descriptions of the males of C. clathrata and C. perroti. Additionally, C. irenae sp. nov. is described in both sexes from southern Africa. Clitaetra biology, so far largely unknown, is presented here based on observations of C. irenae in South Africa, and clitaetrine anatomy is summarized to assess phylogenetic homologies. A species-level phylogenetic analysis of 32 taxa scored for 197 morphological and behavioural characters results in eight most parsimonious cladograms and places Clitaetra as sister to the clade (Herennia+ (Nephilengys+Nephila)). Thus, the orb-weaving spider family Nephilidae Simon contains the (sub)tropical genera Nephila, Nephilengys, Herennia, and Clitaetra, but not Deliochus or Phonognatha. Contra recent cladistic treatments, the nephilines are not tetragnathids, but the sister group to the newly proposed clade, Nephilidae, is ambiguous. The three species clades (subgenera) within Clitaetra show a seemingly old Gondwanan biogeographic pattern: Afroetra subgen. nov., with the three mainland African species, is sister to Clitaetra with the two Indian Ocean island species. Indoetra subgen. nov. contains the unstudied species from Sri Lanka, C. thisbe. Future understanding of the morphology and biology of C. thisbe is important for the polarization of many nephilid features. Vicariance would estimate the clitaetrine subgeneric clades and basal nephilid lineages to be at least 160 Myr old and of Gondwanan origin.
