Definition:
"Variations in the form, composition or structure of the layer of cells that cover the external surface of an organism and form the inner lining between the tissues and organs of that organism and the external environment compared to control. In C. elegans epithelial cells include epithelium of the alimentary tract, intestinal cells, hypodermis, interfacial cells and somatic gonad cells (Wormatlas)." [WB:
WBPerson2021, WB:
WBPerson557]