A coupling system includes two base bodies, each having an aperture for a fluid, an interior predefined circumferential depression and a locking surface. An adapter piece including an aperture for the fluid has two ends and at least two predefined circumferential depressions, which run at least partially along a circumference of the respective ends, wherein the first base body is associated with the first end of the adapter piece and the second base body is associated with the second end of the adapter piece, wherein in a state in which they are pushed inside each other the circumferential depression associated with the respective end of the adapter piece and the interior circumferential depression of the respective base body are located opposite of each other and form a receiving space. In addition, latching elements are provided to prevent the respective latching element from accidentally sliding out of the associated receiving space.