We investigate the three-dimensional evolution of shock impact on a membraneless gas bubble. When a shock wave impacts a gas interface, gas layer is generally perturbed via the Richtmyer-Meshkov instability. We show the vortex structure evolves from the merging process of the extending spikes on the compressed D-shaped surface via the Richtmyer-Meshkov instability. The spikes are found to have a linear growth before 11 μs (of 1.4 mm). A ripple-typed fluctuating ring structure is observed and discussed with the scaling relation. We also notice that a thin layer exists in the intersection of the counterpropagating shock shells. The superposition of the rarefaction waves from both sides of the intersection is suspected to be responsible for the density change.