One of this subfamily's characters is the continuous outline of the pronotum and elytra, which together
extend to cover the legs and head - forming a sort of shield. They are called tortoise beetles or shield beetles (not to be confused with shield bugs).
Most beetles have hard opaque exteriors and fixed colouration. In the Cassidinae, however, at least some of the 'shield' is translucent, enabling the colour of the underlying tissue to be seen. Some species are able to change the colour of that tissue, thereby changing their overall colour. That enables them to camouflage themselves (like a chamaeleon or cuttlefish) or give warnings or make communicating signs (like fireflies and glow-worms).
But there are a lot of species in the Cassidina ...
And there's a problem with that subfamily - they are mostly/all (I think) somewhat rounded in outline.
Your (elongate) specimen is more like Delocrania in shape (from central America) and Ellychnia (occurs in Europe).