Object, comprising at least one surface with at least one opening, wherein a peripheral edge of the surface defining said opening comprises a number of inward extending lips arranged distributed over the periphery of the opening; wherein the peripheral edge of the surface defining said opening of the object is provided with a number of inward extending protrusions arranged distributed over the periphery of the opening between the lips the object being intended and configured to form part of a modular construction system with a coupling element releasably connectable to the object, the coupling element comprising a body with an axial axis arrangeable in the opening, which body is provided along its outer periphery with at least one outward extending locking cam, the coupling element being arrangeable in at least one arranging orientation in the opening of the object, in which arranging orientation the at least one locking cam extends between the lips of the object, and wherein the coupling element is rotatable in the opening relative to the object to at least one locking orientation, in which locking orientation the at least one locking cam engages on a lip of the object such that the coupling element is locked in the opening of the object in an axial direction substantially parallel to the axis of the coupling element; wherein the body of the coupling element is provided over its outer periphery with at least one resiliently movable tongue extending therefrom, to which tongue the locking cam is connected, wherein the protrusions are arranged such that during a rotation of the coupling element between its arranging orientation and its locking orientation the at least one tongue is moved inward by this protrusion, and in the locking orientation the coupling element is locked in a rotational direction. wherein the peripheral edge of the surface defining said opening of the object is provided with a number of inward extending protrusions arranged distributed over the periphery of the opening between the lips the object being intended and configured to form part of a modular construction system with a coupling element releasably connectable to the object, the coupling element comprising a body with an axial axis arrangeable in the opening, which body is provided along its outer periphery with at least one outward extending locking cam, the coupling element being arrangeable in at least one arranging orientation in the opening of the object, in which arranging orientation the at least one locking cam extends between the lips of the object, and wherein the coupling element is rotatable in the opening relative to the object to at least one locking orientation, in which locking orientation the at least one locking cam engages on a lip of the object such that the coupling element is locked in the opening of the object in an axial direction substantially parallel to the axis of the coupling element; wherein the body of the coupling element is provided over its outer periphery with at least one resiliently movable tongue extending therefrom, to which tongue the locking cam is connected, wherein the protrusions are arranged such that during a rotation of the coupling element between its arranging orientation and its locking orientation the at least one tongue is moved inward by this protrusion, and in the locking orientation the coupling element is locked in a rotational direction.