cicala (di mare)
broad, slipper or locust lobster
Really cicala di mare (a cicala is a cicada, or locust). The seagoing version is a small (15cm) relative of the lobster. If you see any they will be imported (frozen) or illegal, as they are protected in Italian waters. A very large one is called a magnosa, and they are rare too.
Or else, they will be canoce, or mantis shrimp. These look like cicale, though they're bigger. They are increasingly popular in Italy, as real cicale are disappearing from the markets, and some people call them cicale out of habit.