LEWIS is the first homogeneous integral-field follow-up spectroscopic survey of 30 extremely LSB galaxies in the Hydra I cluster of galaxies, where the majority of LSB galaxies in the sample (22 in total) are UDGs. LEWIS was approved in 2021, granted with 133.5 hrs at ESO-MUSE@VLT.

Doubling the number of spectroscopically studied UDGs, with the LEWIS project we are making a decisive impact in mapping, for the first time, 

• the 2D stellar kinematics, 

• the stellar population, 

• the GC content and their specific frequency, 

for a complete sample of UDGs in a galaxy cluster with IF spectroscopic data. 

The structural properties together with the baryonic versus DM fraction are used in comparison with hydrodynamical models of UDGs to establish their formation channels as a function of their location in the cluster.