Cytoplasmic intermediate filaments make up the structural component of the cytoskeleton providing mechanical strength to cells. Essential protein required during embryogenesis especially for survival past the L1 larva stage, involved in intestine morphogenesis. Forms some heteromeric filaments with ifb-1. Isoform d is abundantly expressed in the marginal cells of the pharynx, forming apicobasally oriented thick filament bundles that are attached to the apical and basal plasma membrane by hemi-adherens junctions. Expression of isoform c is also seen in the excretory cells and in the uterus. Isoform c is detectable in the amphid sensory neurins and the pharyngeal-intestinal valve. Both isoform c and isoform d are expressed in the rectum and vulva and in some neurons of the tail. In larvae, expression is seen in the excretory cell, the vulva, the rectum and in the thick filament bundles of the pharynx. Expression in pharynx begins in late embryos. Belongs to the intermediate filament family.