Always difficult to identify a crab species definitively. It might well be a gorilla crab, but there are probably a 100 species that could be called a gorilla crab. Two things to remember with small hitchhiker crabs like this. One, the crabs with large, crushing claws can do a lot of damage. Two, that almost all crabs are essentially omnivorous, so even hermits and emerald crabs can sometimes end up eating up something you don't want them to, even if they're put in there for their algae grazing habits. The only exceptions might be the porcelain crab style planktonic feeders, with their very obvious feeding fans, so unlikely to be confused with anything else...
I'd get rid of it.