A releasably attachable seal (200) for a cannula head assembly for use in a trocar system having an obturator, said seal comprising : a support (210) releasably attachable to the cannula head (110) ； a flexible seal (270) disposed within said support and having an aperture (272) for receiving the obturator； an arm (214) outwardly extending from said support； and wherein said arm (214) is movable between a locked position in which said seal is connectable to the cannula head, and an unlocked position in which said seal is removable from the cannula head.
