http://www.slate.com/articles/video/video/2015/09/mantis_shrimp_fights_are_long_brutal_but_not_fatal_video.html

You might expect mantis shrimp, with their rounded claws capable of delivering shockwave-producing blows, to fight each other in short and gory bouts of dominance. But researchers in Biology Letters tell a different story: When mantis shrimp of the same sex were placed in a small tank and fought over a simulated nesting site, the winner was the shrimp with more stamina. Meaning, they don’t need to hit each other harder, so much as keep the punches flying. Hammering away with their raptorial appendages, the tiny crustaceans defended themselves by directing their opponent’s blows toward a region of their tale known as the telson.