Twist-openable dispensing closure accommodating optional liner puncture feature

A dispensing closure system for a container that has an opening to the container interior, said dispensing closure system comprising:

• a body for extending from said container at said opening, said body including (a) a base, (b) a conduit that is reciprocatable relative to said base, and (c) a flexible wall joining said conduit to said base, said conduit including a discharge aperture, a first seal surface, and a sliding seal bead;
• and
• a spout that is carried on, and rotatable relative to, said body and that includes at least one dispensing orifice, a second seal surface for engaging said first seal surface when said conduit is at a predetermined position relative to said base, and a third seal surface for continuously engaging said conduit sliding seal bead;
• said body and spout together defining a rotary-to-linear motion translation drive system that includes a cam track groove on said spout and a cam follower on said conduit for being received in said cam track groove whereby (1) rotation of said spout in one direction moves said conduit in a first direction to a closed position in which said first and second sealing surfaces are in sealing engagement to occlude said spout dispensing orifice, and (2) rotation of said spout in the opposite direction moves said conduit in a second direction opposite from said first direction to an open position in which said conduit first seal surface is spaced from said spout second seal surface to permit flow from said conduit discharge aperture through said spout dispensing orifice, said flexible wall temporarily deforming as said conduit moves between said first and second positions, said flexible wall preventing movement of said conduit in said second direction beyond said open position.