  The study of dynamical processes in protoplanetary disks is essential to
understand planet formation. In this context, transition disks are prime
targets because they are at an advanced stage of disk clearing and may harbor
direct signatures of disk evolution. In this paper, we aim to derive new
constraints on the structure of the transition disk MWC 758, to detect
non-axisymmetric features and understand their origin. We obtained infrared
polarized intensity observations of the protoplanetary disk MWC 758 with
SPHERE/VLT at 1.04 microns to resolve scattered light at a smaller inner
working angle (0.093") and a higher angular resolution (0.027") than previously
achieved. We observe polarized scattered light within 0.53" (148 au) down to
the inner working angle (26 au) and detect distinct non-axisymmetric features
but no fully depleted cavity. The two small-scale spiral features that were
previously detected with HiCIAO are resolved more clearly, and new features are
identified, including two that are located at previously inaccessible radii
close to the star. We present a model based on the spiral density wave theory
with two planetary companions in circular orbits. The best model requires a
high disk aspect ratio (H/r~0.20 at the planet locations) to account for the
large pitch angles which implies a very warm disk. Our observations reveal the
complex morphology of the disk MWC758. To understand the origin of the detected
features, the combination of high-resolution observations in the submillimeter
with ALMA and detailed modeling is needed.
