Glycocalyx is a general term referring to extracellular polymeric material (glycoprotein) produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. External to the plasma membrane, all animal cells have a fuzzy coat called the glycocalyx. This coat consists of the carbohydrate moieties of membrane glycolipids and glycoproteins. Only identical twins have chemically identical glycocalices; everyone else is unique. The glycocalyx is a type of identification that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, and invading organisms. The glycocalyx also includes the cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development. Studies have shown that the glycocalyx plays a role in modulating red blood cell filling in capillaries and it is also believed to be important in many other functions of the vascular system, but studies are ongoing.