Specifically required for the degradation process of misfolded endoplasmic reticulum (ER) luminal proteins. Participates in the transfer of misfolded proteins from the ER to the cytosol, where they are destroyed by the proteasome in a ubiquitin-dependent manner. By endoplasmic reticulum stress. Worms exhibit coelomocyte uptake defective (cup) phenotypes. Coelomocytes are scavenger cells that continuously and non-specifically endocytose fluid from the pseudocoelom (body cavity). Endocytosis by coelomocytes is not essential for growth or survival. Belongs to the derlin family.