part_of part of epithelial cell epithelium cell of epithelium, the layer of cells that cover the external surface of an organism as well as forming an inner lining between the tissues and organs of that organism and the external environment. In C. elegans epithelial cells include epithelium of the alimentary tract, intestinal cells, hypodermis, interfacial cells and somatic gonad cells. WBbt:0003672 worm_anatomy Cell epithelial system