In a phylogeny for the Incurvarioidea proposed by Nielsen and Davis (1985), the Adelidae was placed near the base of the superfamily, distinguished in part from the most basal taxon, Heliozelidae, by the loss of the lateral lagena on the spermatheca. Some mtDNA sequence data also links the problematic North American genus Tridentaforma to this family (Brown et al. 1994). The lateral cervical sclerites of Tridentaforma, however, differ from the typical adelid form.