Context : Debris disks are the intrinsic by-products of the star and planet formation processes .
Most likely due to instrumental limitations and their natural faintness , little is known about debris disks around low mass stars , especially when it comes to spatially resolved observations .

Aims : We present new VLT/SPHERE IRDIS Dual-Polarization Imaging ( DPI ) observations in which we detect the dust ring around the M2 spectral type star TWA 7 .
Combined with additional Angular Differential Imaging observations we aim at a fine characterization of the debris disk and setting constraints on the presence of low-mass planets .

Methods : We model the SPHERE DPI observations and constrain the location of the small dust grains , as well as the spectral energy distribution of the debris disk , using the results inferred from the observations , and perform simple N-body simulations .

Results : We find that the dust density distribution peaks at \sim 0.72 \arcsec ( 25 au ) , with a very shallow outer power-law slope , and that the disk has an inclination of \sim 13 ^ { \circ } with a position angle of \sim 91 ^ { \circ } East of North .
We also report low signal-to-noise detections of an outer belt at a distance of \sim 1.5 \arcsec ( \sim 52 au ) from the star , of a spiral arm in the Southern side of the star , and of a possible dusty clump at 0.11 \arcsec .
These findings seem to persist over timescales of at least a year .
Using the intensity images , we do not detect any planets in the close vicinity of the star , but the sensitivity reaches Jovian planet mass upper limits .
We find that the SED is best reproduced with an inner disk at \sim 0.2 \arcsec ( \sim 7 au ) and another belt at 0.72 \arcsec ( 25 au ) .

Conclusions : We report the detections of several unexpected features in the disk around TWA 7 .
A yet undetected 100 M _ { \oplus } planet with a semi-major axis at 20 - 30 au could possibly explain the outer belt as well as the spiral arm .
We conclude that stellar winds are unlikely to be responsible for the spiral arm .