TARSIS: the Tetra-Armed IFU at Calar Alto designed for the CATARSIS galaxy cluster exploration

In this talk I will present the design of the Integral Field Unit TARSIS, recently selected to be the next generation multi-object spectrograph for the 3.5m telescope at Calar Alto. In addition, I will describe the scientific goals of CATARSIS, the galaxy cluster exploration that will be carried out in the first years of the operation of TARSIS.