A closure assembly for a cell culture apparatus , comprising: a port having an annular sidewall defining an opening in communication with a cell culture chamber of the cell culture apparatus , wherein the sidewall comprises (i) external threads for cooperating with internal threads of a twist cap and (ii) an annularly protruding snap cap engagement feature ; and a snap cap having a top and an annular sidewall extending from the top , wherein the sidewall of the snap cap comprises an inwardly annularly projecting element configured to engage with the annularly protruding snap cap engagement feature of the port such that when fully engaged, the snap cap is not readily removed from the port by unaided human force wherein the annularly protruding snap cap engagement feature of the port has a top surface and a bottom surface , wherein the bottom surface of the engagement feature extends from the sidewall of the port at an angle of less than 110 degrees, and wherein the inwardly annularly projecting element of the snap cap has a top surface and a bottom surface , wherein the top surface of the inwardly annularly projecting element of the snap cap is configured to engage with bottom surface of the engagement feature of the port when a pulling force is applied to the cap , and wherein the top surface of the inwardly annularly projecting element of the snap cap extends from the surface of the sidewall at an angle of less than 110 degrees. a port having an annular sidewall defining an opening in communication with a cell culture chamber of the cell culture apparatus , wherein the sidewall comprises (i) external threads for cooperating with internal threads of a twist cap and (ii) an annularly protruding snap cap engagement feature ; and a snap cap having a top and an annular sidewall extending from the top , wherein the sidewall of the snap cap comprises an inwardly annularly projecting element configured to engage with the annularly protruding snap cap engagement feature of the port such that when fully engaged, the snap cap is not readily removed from the port by unaided human force wherein the annularly protruding snap cap engagement feature of the port has a top surface and a bottom surface , wherein the bottom surface of the engagement feature extends from the sidewall of the port at an angle of less than 110 degrees, and wherein the inwardly annularly projecting element of the snap cap has a top surface and a bottom surface , wherein the top surface of the inwardly annularly projecting element of the snap cap is configured to engage with bottom surface of the engagement feature of the port when a pulling force is applied to the cap , and wherein the top surface of the inwardly annularly projecting element of the snap cap extends from the surface of the sidewall at an angle of less than 110 degrees. wherein the top surface of the inwardly annularly projecting element of the snap cap is configured to engage with bottom surface of the engagement feature of the port when a pulling force is applied to the cap , and wherein the top surface of the inwardly annularly projecting element of the snap cap extends from the surface of the sidewall at an angle of less than 110 degrees. <EOS>