shrimp like critter hitched a ride on branching coraline algae

[duckman]

When I was washing off a branching coraline algae that I received, this critter came off in the RO water I am washing it with. I am guessing it's a shrimp/lobster of some sort but wanted to know if this would be considered a pest or not. If it's not dangerous, I may just let it live in the quarantine tank

 

[Nickp]

Its a mantis shrimp, not something you want in a reef but very cool in its own tank.