I can add a couple more of things about this creatures. They are predators of but also a common prey for bigger fishes and really easy to identify in food chains because the claw hammers are really durable and also exclusive from each species (They are not exclusive from tropical areas, we have several in Europe).

The expected result with a mechanism like this would be the whole claw disintegrating in a couple of shoots by the tension forces applied over the claw. To avoid that they managed somehow to produce one of the strongest structures known in nature just using chitin. The kind of hot stuff that engineers dreams are made.