 They were first identified when EFF-1 mutants were found to "block cell fusion in all epidermal and vulval epithelia" in the roundworm, "Caenorhabditis elegans".EFF-AFF is a family of type I membrane glycoproteins that act as cell–cell fusogens, named from "Anchor cell fusion failure".Because it was known that EFF-1 mutants successfully fused the anchor cell and (uterine seam) utse syncytium to produce a continuous uterine-vulval tube, where these connections failed, AFF-1 mutants were discovered.