  Through an ongoing MUSE program dedicated to study gas removal processes in
galaxies (GAs Stripping Phenomena in galaxies with MUSE, GASP), we have
obtained deep and wide integral field spectroscopy of the galaxy JO171. This
galaxy resembles the Hoag's galaxy, one of the most spectacular examples of
ring galaxies, characterized by a completely detached ring of young stars
surrounding a central old spheroid. At odds with the isolated Hoag's galaxy,
JO171 is part of a dense environment, the cluster Abell 3667, which is causing
gas stripping along tentacles. Moreover, its ring counter-rotates with respect
to the central spheroid. The joint analysis of the stellar populations and the
gas/stellar kinematics shows that the origin of the ring was not due to an
internal mechanism, but was related to a gas accretion event that happened in
the distant past, prior to accretion onto Abell 3667, most probably within a
filament. More recently, since infall in the cluster, the gas in the ring has
been stripped by ram- pressure, causing the quenching of star formation in the
stripped half of the ring. This is the first observed case of ram pressure
stripping in action in a ring galaxy, and MUSE observations are able to reveal
both of the events (accretion and stripping) that caused dramatic
transformations in this galaxy.
