2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14603HI observations have revealed in several shell galaxies the presence of gaseous shells slightly displaced from the stellar shells radially, in the outward direction. We propose a mechanism to form this gaseous shells, based on the well-known phase-wrapping process of the companion matter in a merger, with nearly radial orbits. The mechanism relies on the existence of a clumpy interstellar matter, and on dynamical friction experienced by the companion core.2 pages, 1 figure, in "Galaxy Dynamics: from the Early Universe to the Present", ASP Conf Series, ed. F. Combes, G. Mamon, V. CharmandarisAstrophysicstext