This is the Peacock Mantis Shrimp (Odontodactylus scyllarus), a burrowing predator which subdues its prey by delivering the fastest recorded punch of any living creature. (!) (Other mantis shrimp- members of order Stomatopoda -also share these traits, although the peacock mantis shrimp looks more fabulous while doing it.)
Here’s a youtube video of one of these things beating the hell out of a crab, with commentary by a very educated-sounding
British Australian lady.