Fishermen call this a "thumb splitter." They do not grab their prey but stun it with a "hammer." They strike so quickly that the resulting shockwave does as much damage as the hit. And can also mean that a miss is still "close enough."
Nice detail and comp, Peter. I remember having to remove a mantis shrimp from a mini-reef tank years ago --- definitely don't want them doing that hammer move next to the glass of the aquarium!